public void setBackgroundRGB(int[] rgb) {
            if (rgb.length != 3) {
                throw new RuntimeException();
            }
            backgroundRGB = rgb;
            backgroundSet = true;
        }
Sets the RGB value of the suggested background color.
The <code>rgb</code> parameter should have 3 entries.

<p> The 'bKGD' chunk will encode this information.
plugins/svg-plugin/batik-codec-fix/src/main/java/org/apache/batik/ext/awt/image/codec/png/PNGEncodeParam.java