code: public static int changeColorAlpha(int color, int alpha) {
          int r = (color >> 16) & 0xFF;
          int g = (color >> 8) & 0xFF;
          int b = color & 0xFF;
          return alpha << 24 | r << 16 | g << 8 | b;
      }
docs: Change the color to new alpha
  
  @param color Color
  @param alpha New alpha
  @return New alpha color