Material 3 custom colors - How to generate tonal palettes?

Question

The material 3 site has a section on custom colors.

Theme builder

Is there a way to programmatically generate tonal palettes for a given (harmonized) color to override the color scheme?

@Composable
fun CardMinimalExample(
    customColor: Color = Color.Red
) {
    MaterialTheme(
        colorScheme = MaterialTheme.colorScheme.copy(
            surfaceVariant = customColor
        )
    ) { // inefficient? 
        Card() {
            Text(text = "Hello, world!")
        }
    }
}


@Preview
@Composable
private fun Preview() {
    CardMinimalExample()
}

Answer 1

I found the following restricted method Hct.fromInt that seems to work.

@SuppressLint("RestrictedApi")
@ColorInt
fun getColorRole(@ColorInt color: Int, @IntRange(from = 0, to = 100) tone: Int): Int {
    val hctColor = com.google.android.material.color.utilities.Hct.fromInt(color)
    hctColor.tone = tone.toDouble()
    return hctColor.toInt()
}

    val hexColor = java.lang.String.format("#%08X", -0x1 and color.toArgb())
    Toast
        .makeText(
            context,
            hexColor,
            Toast.LENGTH_SHORT
        )
        .show()

Here is a library built on this method.

data class CustomColorScheme(
    val color: Color,
    val onColor: Color,
    val colorContainer: Color,
    val onColorContainer: Color
)

fun Color.lightCustomColorScheme(): CustomColorScheme {
    val palette = tonalPalette()
    return CustomColorScheme(
        color = palette.color40,
        onColor = palette.color100,
        colorContainer = palette.color90,
        onColorContainer = palette.color10
    )
}

fun Color.darkCustomColorScheme(): CustomColorScheme {
    val palette = tonalPalette()
    return CustomColorScheme(
        color = palette.color80,
        onColor = palette.color20,
        colorContainer = palette.color30,
        onColorContainer = palette.color90
    )
}