The app owns its palette; Material You is opt-in

Context

Material 3 offers dynamic colour: on Android 12+ the scheme is derived from the user’s wallpaper. It looks excellent, it is one line to enable, and it is the default in most templates.

It also means nothing on Android 12+ reads the app’s own colour scheme at all. If dynamic colour is on by default, the palette you designed is invisible on almost every device that runs the app.

Separately, a light/dark override is not a Compose-only problem. The window background is painted from the XML theme before Compose composes anything, and the system-bar scrim is a values-night/ colour resolved at inflation. Both follow Android’s own configuration. So a Compose-only override leaves them following the phone while the app follows the user — visible on API 26–28, where there is no system dark mode to have agreed with by accident.

Decision

Dynamic colour defaults off, behind a Settings toggle. The app’s own scheme is what a user sees unless they ask otherwise.

The scheme is generated, not hand-picked. scripts/gen_scheme.py derives ~36 Material roles from four brand seeds using Material’s own tonal-palette construction (CAM16/HCT), and prints a contrast report. The seeds are the judgement; the roles are arithmetic.

Light/dark is moved in two places, and both are load-bearing: AppTheme picks the Compose scheme, and applyThemeMode calls AppCompatDelegate.setDefaultNightMode to move the configuration, so the window and the bars agree.

Colours come from MaterialTheme, never literals. Spacing comes from theme/Spacing.kt.

Alternatives

Dynamic colour on by default. Free, pretty, and makes the app’s identity invisible where it matters. Also makes any contrast guarantee unverifiable — you cannot check a palette you do not control.

Hand-pick the roles. Breaks the fixed tonal relationship each role holds with its family, and the failure surfaces as a contrast bug on one screen out of thirty rather than as a visible mistake in the palette file.

Compose-only dark mode. Leaves the window background and the bar scrim following the phone.

Consequences

• theme/Color.kt is generated. Never edit a role; edit the seeds and re-run.
• applyThemeMode must be called from MainApplication.onCreate — before any Activity exists, so the first window is right — and from the Settings toggle. It is process-wide and process-only: AppCompat persists an application locale but not a night mode, which is why AppPreferences stores it and why the call is repeated on every cold start.
• The startup theme is read with one blocking DataStore read, deliberately. A Flow collected in a composition arrives a frame late, which is a visible light flash on every cold start for a user who chose dark.
• The system-bar scrim lives in four colors.xml qualifiers, not in a style. night outranks vN in Android’s qualifier precedence, so values-night/ would beat values-v29/ on an API 29+ phone in dark mode; values-night-v29/ is what settles it, and a <style> cannot merge across qualified files the way one <color> reference can.