颜色转换，变暗效果。可用于按钮点击效果。 Convert the color, return the new color that dark than before. this can be used for btn click preview.

ColorUtils.java

 public static int manipulateColor(int color, float rFactor, float gFactor, float bFactor) {
    int a = Color.alpha(color);
    int r = Math.round(Color.red(color) * rFactor);
    int g = Math.round(Color.green(color) * gFactor);
    int b = Math.round(Color.blue(color) * bFactor);
    return Color.argb(a,
            Math.min(r, 255),
            Math.min(g, 255),
            Math.min(b, 255));
}

public static void example() {
  int color = Color.argb(255, 244, 68, 68);
  int colorDark = manipulateColor(color, 0.8f, 0.6f, 0.6f);
}