I find myself once again publishing smaller versions of apps as a result of a core need in another app. This time as a wallpaper manager called Prism. I won’t bore you with the details but getting access to the Wallpaper on Android requires elevated permissions, permissions which I didn’t want to ask for in the first place.

I put together something that I think every wallpaper app should do, expose a way for third-party apps to access the wallpaper if the user permits it. Anyway, that’s not why we’re here.

Part of designing a new app is that I get to play around with the design aesthetic, each time I can do something slightly different. I had just created a new Compose project and was removing some boilerplate and came across this chunk in the Default Theme file:

@Composable
fun MyApplicationTheme(
    darkTheme: Boolean = isSystemInDarkTheme(),
    // Dynamic color is available on Android 12+
    dynamicColor: Boolean = true,
    content: @Composable () -> Unit
) {
    val colorScheme = when {
        dynamicColor && Build.VERSION.SDK_INT >= Build.VERSION_CODES.S -> {
            val context = LocalContext.current
            if (darkTheme) dynamicDarkColorScheme(context) else dynamicLightColorScheme(context)
        }

        darkTheme -> DarkColorScheme
        else -> LightColorScheme
    }

    MaterialTheme(
        colorScheme = colorScheme,
        typography = Typography,
        content = content
    )
}

Clicking through into dynamicDarkColorScheme I saw:

@RequiresApi(34)
internal fun dynamicDarkColorScheme34(context: Context) = darkColorScheme(
    primary = ColorResourceHelper.getColor(context, android.R.color.system_primary_dark),

The android.R.color.system_primary_dark is resolved by the system. With some digging, I stumbled on @android:color/system_accent1_* variants.

Given that I was building a Wallpaper Manager, and Wallpapers are an input into Material You (great article here on the relationship), I wanted to see if there was something fun I could do. As I was building the launcher icon for Prism, I wondered if I could use the theme resource colors in any interesting ways.

The promise was that I could use this resource identifier, and the system would swap it to a Material You derived color.

I started with the monochrome icon and a simple color: system_accent1_700.

<vector xmlns:android="<http://schemas.android.com/apk/res/android>"
    android:width="108dp"
    android:height="108dp"
    android:viewportWidth="108"
    android:viewportHeight="108">

    <group
        android:scaleX="1.25"
        android:scaleY="1.25"
        android:translateX="25"
        android:translateY="24">
        <path
            **android:fillColor="@android:color/system_accent1_400"**
            android:fillType="nonZero"
            android:pathData="M17.478,41.67c0.334,0.33 0.84,0.422 1.272,0.233L39.32,32.87c0.308,-0.135 0.54,-0.397 0.634,-0.717 0.094,-0.32 0.04,-0.664 -0.147,-0.94l-16,-23.71a1.147,1.147 0,0 0,-0.99 -0.502,1.145 1.145,0 0,0 -0.953,0.568L8.15,31.279c-0.256,0.442 -0.18,0.998 0.184,1.358l9.143,9.032ZM17.468,38.466 L10.568,31.65 20.918,13.758 17.468,38.466ZM23.578,11.232 L37.154,31.351 19.698,39.015 23.578,11.232Z" />
    </group>
</vector>

I built and launched the app, and noticed that the color didn't change, but when I opened the app, the themed color was being used. It’s also used when re-arranging the icon in the launcher.

Turns out this is because the AOSP/Pixel launcher caches the launcher images and doesn’t quite update them when the wallpaper changes. You can force a change by toggling “Themed Icons”. Perhaps for obvious reasons, before Material You there was no need to flush the icon cache.

Armed with this information, I got more ambitious and landed on a new icon. One which captured the spirit of the app’s name a bit better.

• Code

Looks pretty cool with the Material You inspired colors. I’m sure someone has done something like this already, but it was fun to rediscover!