public class ColoredFiller implements Component {
  private final Brush color;

  public ColoredFiller(Brush color) {
    this.color = color.asOpaque();  // implicit nullcheck
  }

  @Override
  public void paint(CanvasArea area, Rect zone) {
    area.drawRectangle(zone.x, zone.y, zone.width, zone.height, color);
  }
}