To create your own themes for Live 12 I found you can do the following:
Method 1
Method 2
Generate a theme interactively here and then upload it to the folder mentioned in the above method.
Method 3
Spotify theme is boss 
Here’s the modified version for live 12, copy and save it as Spotify.ask:
<?xml version="1.0" encoding="UTF-8"?>
<Ableton MajorVersion="5" MinorVersion="12.0_12049" SchemaChangeCount="3" Creator="Ableton Live 12.0d1" Revision="">
<Theme>
<ControlForeground Value="#6b6b6b" />
<TextDisabled Value="#787878" />
<ControlDisabled Value="#212121" />
<MeterBackground Value="#1e1e1e" />
<SurfaceHighlight Value="#1c1c1c" />
<SurfaceArea Value="#141414" />
<Desktop Value="#1f1f1f" />
<ViewCheckControlEnabledOn Value="#525252" />
<ScrollbarInnerHandle Value="#424242" />
<ScrollbarInnerTrack Value="#242424" />
<ScrollbarOuterHandle Value="#828282" />
<ScrollbarOuterTrack Value="#a0a0a0" />
<ScrollbarLCDHandle Value="#a0a0a0" />
<ScrollbarLCDTrack Value="#a0a0a0" />
<DetailViewBackground Value="#555555" />
<PreferencesTab Value="#414141" />
<SelectionFrame Value="#d2d2d2" />
<ControlBackground Value="#555555" />
<ControlFillHandle Value="#555555" />
<ChosenDefault Value="#8b8d8b" />
<ChosenRecord Value="#ff2b0f" />
<ChosenPreListen Value="#3eda50" />
<ImplicitArm Value="#ff0000" />
<RangeDefault Value="#3eda50" />
<RangeDisabled Value="#828282" />
<RangeDisabledOff Value="#323232" />
<LearnMidi Value="#4034ef" />
<LearnKey Value="#ffbc44" />
<LearnMacro Value="#00ff81" />
<RangeEditField Value="#121614" />
<RangeEditField2 Value="#8b4b47" />
<BipolReset Value="#6dd7ff" />
<ChosenAlternative Value="#6dd7ff" />
<ChosenAlert Value="#ff6446" />
<ChosenPlay Value="#00ff81" />
<Clip1 Value="#8b7936" />
<Clip2 Value="#999565" />
<Clip3 Value="#b8ce93" />
<Clip4 Value="#afb95b" />
<Clip5 Value="#52ba46" />
<Clip6 Value="#81d24c" />
<Clip7 Value="#6baace" />
<Clip8 Value="#4881aa" />
<Clip9 Value="#954eb2" />
<Clip10 Value="#ff5f80" />
<Clip11 Value="#dc4848" />
<Clip12 Value="#d66b18" />
<Clip13 Value="#e0aa2a" />
<Clip14 Value="#ffec75" />
<Clip15 Value="#e7e6e6" />
<Clip16 Value="#a0a0a0" />
<ClipText Value="#000000" />
<ClipBorder Value="#ffffff" />
<SelectionBackground Value="#c7edff" />
<StandbySelectionBackground Value="#2b2b2b" />
<SelectionForeground Value="#3eda50" />
<StandbySelectionForeground Value="#3eda50" />
<SurfaceBackground Value="#171717" />
<AutomationColor Value="#ff584c" />
<AutomationGrid Value="#000000" />
<LoopColor Value="#a0a0a0" />
<OffGridLoopColor Value="#b4b4b4" />
<ArrangementRulerMarkings Value="#a0a0a0" />
<DetailViewRulerMarkings Value="#d2d2d2" />
<ShadowDark Value="#000000" />
<ShadowLight Value="#555555" />
<DisplayBackground Value="#282828" />
<AbletonColor Value="#00ff00" />
<WaveformColor Value="#000000" />
<VelocityColor Value="#ff584c" />
<Alert Value="#ff6446" />
<ControlOnForeground Value="#3f3636" />
<ControlOffForeground Value="#737373" />
<ControlOnDisabledForeground Value="#323232" />
<ControlOffDisabledForeground Value="#8c8c8c" />
<ControlOnAlternativeForeground Value="#141414" />
<ControlTextBack Value="#1f1f1f" />
<ControlContrastFrame Value="#1e1e1e" />
<ControlSelectionFrame Value="#1e1e1e" />
<ControlContrastTransport Value="#282828" />
<Progress Value="#ffb532" />
<ProgressText Value="#646464" />
<TransportProgress Value="#af831f" />
<ClipSlotButton Value="#282828" />
<BrowserBar Value="#242424" />
<BrowserBarOverlayHintTextColor Value="#636363" />
<BrowserDisabledItem Value="#828282" />
<BrowserSampleWaveform Value="#6e6e6e" />
<AutomationDisabled Value="#a0a0a0" />
<AutomationMouseOver Value="#5dbbd8" />
<MidiNoteMaxVelocity Value="#ff584c" />
<RetroDisplayBackground Value="#0f0f0f" />
<RetroDisplayBackgroundLine Value="#464646" />
<RetroDisplayForeground Value="#3eda50" />
<RetroDisplayForeground2 Value="#c9c9c9" />
<RetroDisplayForegroundDisabled Value="#8c8c8c" />
<RetroDisplayGreen Value="#ffb532" />
<RetroDisplayRed Value="#3b3b3b" />
<RetroDisplayHandle1 Value="#3ff354" />
<RetroDisplayHandle2 Value="#eda59f" />
<RetroDisplayScaleText Value="#ffffff" />
<ThresholdLineColor Value="#6dd7ff" />
<GainReductionLineColor Value="#ffb532" />
<InputCurveColor Value="#ffffff" />
<InputCurveOutlineColor Value="#000000" />
<OutputCurveColor Value="#d6dde4" />
<OutputCurveOutlineColor Value="#edf0f4" />
<SpectrumDefaultColor Value="#4b4b4b" />
<SpectrumAlternativeColor Value="#2b64bf" />
<SpectrumGridLines Value="#383838" />
<Operator1 Value="#fddb04" />
<Operator2 Value="#3de004" />
<Operator3 Value="#1effab" />
<Operator4 Value="#ff9204" />
<DrumRackScroller1 Value="#323232" />
<DrumRackScroller2 Value="#282828" />
<FilledDrumRackPad Value="#828282" />
<SurfaceAreaFocus Value="#141414" />
<FreezeColor Value="#2b64bf" />
<GridLabel Value="#000000" />
<ArrangerGridTiles Value="#1a1a1a" />
<DetailGridTiles Value="#000000" />
<GridGuideline Value="#c3c3c3" />
<OffGridGuideline Value="#ffffff" />
<TreeColumnHeadBackground Value="#292929" />
<TreeColumnHeadForeground Value="#808080" />
<TreeColumnHeadSelected Value="#505050" />
<TreeColumnHeadFocus Value="#555555" />
<TreeColumnHeadControl Value="#282828" />
<TreeRowCategoryForeground Value="#828282" />
<TreeRowCategoryBackground Value="#000000" />
<SearchIndication Value="#ffcd73" />
<SearchIndicationStandby Value="#a98e5c" />
<KeyZoneBackground Value="#cdd8b3" />
<KeyZoneCrossfadeRamp Value="#86a837" />
<VelocityZoneBackground Value="#dab4b4" />
<VelocityZoneCrossfadeRamp Value="#da4e4e" />
<SelectorZoneBackground Value="#b4ccda" />
<SelectorZoneCrossfadeRamp Value="#5577c6" />
<ViewCheckControlEnabledOff Value="#d2d2d2" />
<ViewCheckControlDisabledOn Value="#d2d2d2" />
<ViewCheckControlDisabledOff Value="#d2d2d2" />
<BackgroundClip Value="#6c6c6c" />
<BackgroundClipFrame Value="#252525" />
<WarperTimeBarRulerBackground Value="#414141" />
<WarperTimeBarMarkerBackground Value="#373737" />
<BipolarPotiTriangle Value="#1e1e1e" />
<Poti Value="#1e1e1e" />
<DeactivatedPoti Value="#323232" />
<PotiNeedle Value="#1e1e1e" />
<DeactivatedPotiNeedle Value="#323232" />
<TransportOffBackground Value="#282828" />
<TransportOffDisabledForeground Value="#555555" />
<TransportSelectionBackground Value="#414141" />
<GridLineBase Value="#000000" />
<Modulation Value="#6dd7ff" />
<ModulationDisabled Value="#c8c8c8" />
<ModulationMouseOver Value="#4aa1ff" />
<AutomationTransformToolFrame Value="#000000" />
<AutomationTransformToolFrameActive Value="#000000" />
<AutomationTransformToolHandle Value="#000000" />
<AutomationTransformToolHandleActive Value="#000000" />
</Theme>
</Ableton>I tried your theme but it is messed up in live 12 for me!
You are correct! I didn’t test the example.
I messed around and came up with the following theme which does work in 12:
<?xml version="1.0" encoding="UTF-8"?>
<Ableton MajorVersion="5" MinorVersion="12.0_12049" SchemaChangeCount="3" Creator="Ableton Live 12.0d1" Revision="">
<Theme>
<ControlForeground Value="#cbcbcd" />
<TextDisabled Value="#7d8088" />
<ControlDisabled Value="#7d8088" />
<MeterBackground Value="#121417" />
<SurfaceHighlight Value="#40434b" />
<SurfaceArea Value="#1d1f23" />
<Desktop Value="#22242a" />
<ViewCheckControlEnabledOn Value="#44FF05" />
<ScrollbarInnerHandle Value="#6d7079" />
<ScrollbarInnerTrack Value="#00000000" />
<ScrollbarLCDHandle Value="#6d7079" />
<ScrollbarLCDTrack Value="#2f3138" />
<ScrollbarMixerShowOnScrollHandle Value="#00000066" />
<DetailViewBackground Value="#373a41" />
<PreferencesTab Value="#2f3138" />
<SelectionFrame Value="#7d8088" />
<ControlBackground Value="#18191e" />
<ControlFillHandle Value="#5c6069" />
<ChosenDefault Value="#44FF05" />
<ChosenRecord Value="#ff5559" />
<ChosenPreListen Value="#3c6ab6" />
<ImplicitArm Value="#ff000064" />
<RangeDefault Value="#44FF05" />
<RangeDisabled Value="#7d8088" />
<RangeDisabledOff Value="#656871" />
<LearnMidi Value="#4034ef" />
<LearnKey Value="#ff6400" />
<LearnMacro Value="#00da48" />
<RangeEditField Value="#008493" />
<RangeEditField2 Value="#9e9e9e" />
<BipolReset Value="#44FF05" />
<ChosenAlternative Value="#44FF05" />
<ChosenAlert Value="#e76942" />
<ChosenPlay Value="#00d38d" />
<Clip1 Value="#8b7936" />
<Clip2 Value="#999565" />
<Clip3 Value="#b8ce93" />
<Clip4 Value="#afb95b" />
<Clip5 Value="#52ba46" />
<Clip6 Value="#81d24c" />
<Clip7 Value="#6baace" />
<Clip8 Value="#4881aa" />
<Clip9 Value="#954eb2" />
<Clip10 Value="#ff5f80" />
<Clip11 Value="#dc4848" />
<Clip12 Value="#d66b18" />
<Clip13 Value="#e0aa2a" />
<Clip14 Value="#ffec75" />
<Clip15 Value="#e7e6e6" />
<Clip16 Value="#a0a0a0" />
<ClipText Value="#000000" />
<ClipBorder Value="#22242a" />
<SceneContrast Value="#22242a" />
<SelectionBackground Value="#525354" />
<StandbySelectionBackground Value="#303336" />
<SelectionForeground Value="#44FF05" />
<StandbySelectionForeground Value="#44FF05" />
<SelectionBackgroundContrast Value="#819499" />
<SurfaceBackground Value="#2f3138" />
<TakeLaneTrackHighlighted Value="#373a41" />
<TakeLaneTrackNotHighlighted Value="#282b31" />
<AutomationColor Value="#44FF05" />
<AutomationGrid Value="#07080a" />
<LoopColor Value="#a1a3a9" />
<OffGridLoopColor Value="#94949b4f" />
<ArrangementRulerMarkings Value="#a1a3a9" />
<DetailViewRulerMarkings Value="#a1a3a9" />
<ShadowDark Value="#1e1e2454" />
<ShadowLight Value="#22242bcc" />
<DisplayBackground Value="#121417" />
<AbletonColor Value="#00ff00" />
<WaveformColor Value="#121417ef" />
<DimmedWaveformColor Value="#6d7079df" />
<VelocityColor Value="#e95449" />
<VelocitySelectedOrHovered Value="#5b8cff" />
<NoteProbability Value="#656871" />
<Alert Value="#e76942" />
<ControlOnForeground Value="#141414" />
<ControlOffForeground Value="#cbcbcd" />
<ControlOnDisabledForeground Value="#1d1f23" />
<ControlOffDisabledForeground Value="#6d7079" />
<ControlOnAlternativeForeground Value="#44FF05" />
<ControlTextBack Value="#1d1f23" />
<ControlContrastFrame Value="#0c0d10" />
<ControlSelectionFrame Value="#a1a3a9" />
<ControlContrastTransport Value="#2f3138" />
<ViewControlOn Value="#44FF05" />
<ViewControlOff Value="#40434b" />
<Progress Value="#44FF05" />
<ProgressText Value="#656871" />
<TransportProgress Value="#44FF05" />
<ClipSlotButton Value="#18191e" />
<BrowserBar Value="#2f3138" />
<BrowserBarOverlayHintTextColor Value="#5c6069" />
<BrowserDisabledItem Value="#7d8088" />
<BrowserSampleWaveform Value="#93959c" />
<AutomationDisabled Value="#7d7d7d" />
<AutomationMouseOver Value="#ffd1ff" />
<MidiNoteMaxVelocity Value="#e95449" />
<RetroDisplayBackground Value="#121417" />
<RetroDisplayBackgroundLine Value="#373a41" />
<RetroDisplayForeground Value="#44FF05" />
<RetroDisplayForeground2 Value="#44FF05" />
<RetroDisplayForegroundDisabled Value="#93959c" />
<RetroDisplayGreen Value="#44FF05" />
<RetroDisplayRed Value="#44FF05" />
<RetroDisplayHandle1 Value="#44FF05" />
<RetroDisplayHandle2 Value="#ffffff" />
<RetroDisplayScaleText Value="#93959c" />
<RetroDisplayTitle Value="#cbcbcd" />
<ThresholdLineColor Value="#44FF05" />
<GainReductionLineColor Value="#44FF05" />
<InputCurveColor Value="#51545d" />
<InputCurveOutlineColor Value="#00000000" />
<OutputCurveColor Value="#94949a4c" />
<OutputCurveOutlineColor Value="#d4d5d6" />
<SpectrumDefaultColor Value="#51545d" />
<SpectrumAlternativeColor Value="#3c6ab6" />
<SpectrumGridLines Value="#cacace3f" />
<Operator1 Value="#e0d825" />
<Operator2 Value="#29d6cd" />
<Operator3 Value="#6571f6" />
<Operator4 Value="#f3751b" />
<DrumRackScroller1 Value="#40434b" />
<DrumRackScroller2 Value="#6d7079" />
<FilledDrumRackPad Value="#cbcbcd" />
<SurfaceAreaFocus Value="#1d1f23" />
<FreezeColor Value="#4391e6" />
<GridLabel Value="#cbcbcd7f" />
<GridLineBase Value="#03060654" />
<ArrangerGridTiles Value="#0a0a0a19" />
<DetailGridTiles Value="#0a0a0a19" />
<GridGuideline Value="#cbcbcd" />
<OffGridGuideline Value="#cbcbcf4f" />
<TreeColumnHeadBackground Value="#40434b" />
<TreeColumnHeadForeground Value="#cbcbcd" />
<TreeColumnHeadSelected Value="#40434b" />
<TreeColumnHeadFocus Value="#40434b" />
<TreeColumnHeadControl Value="#7d8088" />
<TreeRowCategoryForeground Value="#7d8088" />
<TreeRowCategoryBackground Value="#00000000" />
<BrowserTagBackground Value="#1d1f23" />
<SearchIndication Value="#ecca6d" />
<KeyZoneBackground Value="#acf6b4" />
<KeyZoneCrossfadeRamp Value="#28bd56" />
<VelocityZoneBackground Value="#f5a7a3" />
<VelocityZoneCrossfadeRamp Value="#e95449" />
<SelectorZoneBackground Value="#bed6f4" />
<SelectorZoneCrossfadeRamp Value="#2d66d2" />
<ViewCheckControlEnabledOff Value="#7d8088" />
<ViewCheckControlDisabledOn Value="#93959c" />
<ViewCheckControlDisabledOff Value="#5c6069" />
<DefaultBlendFactor Value="0.7570000291" />
<IconBlendFactor Value="0.7300000191" />
<ClipBlendFactor Value="0.7580000162" />
<NoteBorderStandbyBlendFactor Value="0.5360000134" />
<RetroDisplayBlendFactor Value="1" />
<CheckControlNotCheckedBlendFactor Value="0.5" />
<MixSurfaceAreaBlendFactor Value="0.375" />
<TextFrameSegmentBlendFactor Value="0.3950000107" />
<NoteDisabledSelectedBlendFactor Value="0.5" />
<BackgroundClip Value="#5c6069" />
<BackgroundClipFrame Value="#2f3138" />
<WarperTimeBarRulerBackground Value="#2f3138" />
<WarperTimeBarMarkerBackground Value="#282b31" />
<MinVelocityNoteBlendFactor Value="0.2639999986" />
<StripedBackgroundShadeFactor Value="0.8999999762" />
<NonEditableAutomationAlpha Value="127" />
<DisabledContextMenuIconAlpha Value="85" />
<ClipBorderAlpha Value="120" />
<ScrollBarAlpha Value="255" />
<ScrollBarOnHoverAlpha Value="255" />
<ScrollBarBackgroundAlpha Value="255" />
<InaudibleTakeLightness Value="0.322000000000000008" />
<InaudibleTakeSaturation Value="0.775000000000000022" />
<InaudibleTakeNameLightness Value="0.800000000000000044" />
<InaudibleTakeNameSaturation Value="0.853999999999999981" />
<AutomationLaneClipBodyLightness Value="0.260000000000000009" />
<AutomationLaneClipBodySaturation Value="0.80600000000000005" />
<AutomationLaneHeaderLightness Value="0.251000000000000001" />
<AutomationLaneHeaderSaturation Value="0.53400000000000003" />
<TakeLaneHeaderLightness Value="0.479999999999999982" />
<TakeLaneHeaderSaturation Value="0.900000000000000022" />
<TakeLaneHeaderNameLightness Value="0.849999999999999978" />
<TakeLaneHeaderNameSaturation Value="0.900000000000000022" />
<AutomationLaneHeaderNameLightness Value="0.708999999999999964" />
<AutomationLaneHeaderNameSaturation Value="0.900000000000000022" />
<ClipContrastColorAdjustment Value="24" />
<SessionSlotOklabLCompensationFactor Value="20" />
<BipolarPotiTriangle Value="#0c0d10" />
<Poti Value="#0c0d10" />
<DeactivatedPoti Value="#22242a" />
<PotiNeedle Value="#121417" />
<DeactivatedPotiNeedle Value="#22242a" />
<PianoBlackKey Value="#40434b" />
<PianoWhiteKey Value="#93959c" />
<PianoKeySeparator Value="#40434b" />
<TransportOffBackground Value="#2f3138" />
<TransportOffDisabledForeground Value="#6d7079" />
<TransportOffForeground Value="#cbcbcd" />
<TransportSelectionBackground Value="#5c6069" />
<Modulation Value="#009aac" />
<ModulationDisabled Value="#79bdc7a9" />
<ModulationMouseOver Value="#8cffff" />
<AutomationTransformToolFrame Value="#212429bf" />
<AutomationTransformToolFrameActive Value="#07080a" />
<AutomationTransformToolHandle Value="#212429bf" />
<AutomationTransformToolHandleActive Value="#07080a" />
<MutedAuditionClip Value="#656871" />
<LinkedTrackHover Value="#b3d4e5" />
<ExpressionLaneHeaderHighlight Value="#373a41" />
<DeactivatedClipHeader Value="#6d7079df" />
<DeactivatedClipHeaderForeground Value="#22242a" />
<ScaleAwareness Value="#b595fc" />
<StandardVuMeter>
<OnlyMinimumToMaximum Value="false" />
<Maximum Value="#ff0a0a" />
<AboveZeroDecibel Value="#ff0a0a" />
<ZeroDecibel Value="#ff0a0a" />
<BelowZeroDecibel1 Value="#ffd100" />
<BelowZeroDecibel2 Value="#00f758" />
<Minimum Value="#00f758" />
</StandardVuMeter>
<OverloadVuMeter>
<OnlyMinimumToMaximum Value="true" />
<Maximum Value="#ff0a0a" />
<AboveZeroDecibel Value="#ffffff" />
<ZeroDecibel Value="#ffffff" />
<BelowZeroDecibel1 Value="#ffffff" />
<BelowZeroDecibel2 Value="#ffffff" />
<Minimum Value="#af0a0a" />
</OverloadVuMeter>
<DisabledVuMeter>
<OnlyMinimumToMaximum Value="false" />
<Maximum Value="#ff0a0a" />
<AboveZeroDecibel Value="#ffd00a" />
<ZeroDecibel Value="#828282" />
<BelowZeroDecibel1 Value="#7e7e7e" />
<BelowZeroDecibel2 Value="#7b7b7b" />
<Minimum Value="#6e6e6e" />
</DisabledVuMeter>
<HeadphonesVuMeter>
<OnlyMinimumToMaximum Value="false" />
<Maximum Value="#a5a5f1" />
<AboveZeroDecibel Value="#90aaec" />
<ZeroDecibel Value="#90aaec" />
<BelowZeroDecibel1 Value="#85b8f1" />
<BelowZeroDecibel2 Value="#7cc6f5" />
<Minimum Value="#0affff" />
</HeadphonesVuMeter>
<SendsOnlyVuMeter>
<OnlyMinimumToMaximum Value="false" />
<Maximum Value="#c8c800" />
<AboveZeroDecibel Value="#c8c800" />
<ZeroDecibel Value="#6464ff" />
<BelowZeroDecibel1 Value="#6464ff" />
<BelowZeroDecibel2 Value="#6464ff" />
<Minimum Value="#6464ff" />
</SendsOnlyVuMeter>
<BipolarGainReductionVuMeter>
<OnlyMinimumToMaximum Value="false" />
<Maximum Value="#5577c6" />
<AboveZeroDecibel Value="#5577c6" />
<ZeroDecibel Value="#ffa519" />
<BelowZeroDecibel1 Value="#ffa519" />
<BelowZeroDecibel2 Value="#ffa519" />
<Minimum Value="#ffa519" />
</BipolarGainReductionVuMeter>
<OrangeVuMeter>
<OnlyMinimumToMaximum Value="true" />
<Maximum Value="#ffa519" />
<AboveZeroDecibel Value="#ffa519" />
<ZeroDecibel Value="#ffa519" />
<BelowZeroDecibel1 Value="#ffa519" />
<BelowZeroDecibel2 Value="#ffa519" />
<Minimum Value="#ffa519" />
</OrangeVuMeter>
<MainViewFocusIndicator Value="#7d8088" />
<MidiEditorBlackKeyBackground Value="#07070726" />
<MidiEditorBackgroundWhiteKeySeparator Value="#00000a19" />
<RangeEditField3 Value="#7c4960" />
<ScrollbarInnerHandleHover Value="#7d8088" />
<ScrollbarInnerTrackHover Value="#1d1f23" />
<ScrollbarLCDHandleHover Value="#7d8088" />
<ScrollbarLCDTrackHover Value="#40434b" />
<ScrollbarMixerShowOnScrollHandleHover Value="#0000007f" />
</Theme>
</Ableton>I’m using this one, it’s good. Will probably try to create a slightly darker version like the original too if I get around to it…
