code: public void setColorGradient(int x1, int y1, ColorRgba color1, int x2, int y2, ColorRgba color2)
      {
          gradientColor = new ColorGradient(x1, y1, color1, x2, y2, color2);
      }
docs: Set a gradient color from point 1 with color 1 to point2 with color 2.
  
  @param x1 The first horizontal location.
  @param y1 The first vertical location.
  @param color1 The first color.
  @param x2 The last horizontal location.
  @param y2 The last vertical location.
  @param color2 The last color.