private val LightColorPalette = lightColors(
    surface = Color.Red,
    onSurface = Color.White,
)

@Composable
fun CustomTheme(
    content: @Composable () -> Unit
) {

  MaterialTheme(
      colors = LightColorPalette,
      typography = typography,
      shapes = shapes,
      content = content
  )
}

LocalContentAlpha provides ContentAlpha.high

private fun contentAlpha(
        /*@FloatRange(from = 0.0, to = 1.0)*/
        highContrastAlpha: Float,
        /*@FloatRange(from = 0.0, to = 1.0)*/
        lowContrastAlpha: Float
    ): Float {
        val contentColor = LocalContentColor.current
        val lightTheme = MaterialTheme.colors.isLight
        return if (lightTheme) {
            if (contentColor.luminance() > 0.5) highContrastAlpha else lowContrastAlpha
        } else {
            if (contentColor.luminance() < 0.5) highContrastAlpha else lowContrastAlpha
        }
    }

I believe this is how it works, though I’m not sure if the use case of setting light on dark colors was considered in a light theme