code: public void setGradationColor(GradationMode2D mode, Color color1, Color color2) {
          setGradation(true);
          if (startColor == null || endColor == null) {
              startColor = new RGBColor(0.0, 0.0, 0.0);
              endColor = new RGBColor(0.0, 0.0, 0.0);
          }
          startColor = color1;
          endColor = color2;
          this.mode = mode;
      }
docs: Sets the gradation mode and colors.
  
  @param mode The mode of gradation.
  @param color1 The color for gradation.
  @param color2 The color for gradation.
  
  @see casmi.GradationMode2D