code: public void setCenterColor(ColorSet colorSet) {
          if (this.centerColor == null) {
              this.centerColor = new RGBColor(0.0, 0.0, 0.0);
          }
          setGradation(true);
          this.centerColor = RGBColor.color(colorSet);
      }
docs: Sets the colorSet of the center of this Arc.
  
  @param colorSet The colorSet of the center of the Arc.