public void setBackgroundGray(int gray) {
            backgroundPaletteGray = gray;
            backgroundSet = true;
        }
Sets the suggested gray level of the background.

<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