Material's Colors has all its fields as a state - documented as an optimization to when the color changes not to recompose everything, but only composables depending on the particular color. But I can't find any place that would modify any color. So is this a preoptimized for some user-land use-cases? And what they could be?

Animating theme colors

Is such animation used in compose? The only one I can think of is going from light to dark. Or any other reason?

Jetcaster animates the

primary

color of the app depending on the podcast artwork, for a real-life example https://github.com/android/compose-samples/tree/master/Jetcaster

Thanks, great example!

Exactly,

MaterialTheme

internally modifies the state, it's a performance optimization for the internals, but isn't consumer facing https://cs.android.com/androidx/platform/frameworks/support/+/androidx-master-dev:compose/material/material/src/commonMain/kotlin/androidx/compose/material/MaterialTheme.kt;l=63 Internally we just update the initial theme provided, with colors from the new object, instead of replacing the object in the ambient value

Oh, I see it. I think the trick is here:

val rememberedColors = remember {
    // TODO: b/162450508 remove the unnecessary .copy() here when it isn't needed to ensure that
    // we don't skip the updateColorsFrom call
    colors.copy()
}.apply { updateColorsFrom(colors) }