@Override
  public int getOpacity() {
    return DrawableUtils.getOpacityFromColor(DrawableUtils.multiplyColorAlpha(mColor, mAlpha));
  }
Returns the opacity of the final color which would be used for drawing. This has been inspired
by Android ColorDrawable.

@return the opacity
drawee/src/main/java/com/facebook/drawee/drawable/RoundedColorDrawable.java