static Color withOpacity(Color c, double alpha) {
  ret colorWithAlpha(c, alpha);
}



static Color withOpacity(double alpha, Color c) {
  ret colorWithAlpha(alpha, c);
}

// opacity = 0 to 255
static int withOpacity(int opacity, int rgb) {
  ret (opacity << 24) | (rgb & 0xFFFFFF);
}