Create color for use in TreeItem, v.2

private Image createImage(int imageSize)
{
    Image image = new Image(Display.getDefault(), imageSize, imageSize);
    GC gc = new GC(image);
    gc.setAntialias(SWT.ON);
    gc.setBackground(... the color ...);
    gc.fillRoundRectangle(0, 0, imageSize, imageSize, 5, 5);
    gc.dispose();

    ImageData data = image.getImageData();
    data.transparentPixel = data.palette.getPixel(new RGB(255, 255, 255));
    return new Image(Display.getDefault(), data);
}