Bug 184423 [JFace] ColorRegistry.getRGB(String) can return null
I20070427-0010 ColorRegistry.getRGB(String) can return null but this is not speced in the Javadoc.
bundles/org.eclipse.jface/src/org/eclipse/jface/resource/ColorRegistry.java
/**
     * This registries <code>Display</code>. All colors will be allocated using 
     * it.
     */
    protected Display display;
    /**
     * Collection of <code>Color</code> that are now stale to be disposed when 
     * it is safe to do so (i.e. on shutdown).
     */
    private List staleColors = new ArrayList();
    /**
     * Table of known colors, keyed by symbolic color name (key type: <code>String</code>,
     * value type: <code>org.eclipse.swt.graphics.Color</code>.
     */
    private Map stringToColor = new HashMap(7);
    /**
     * Table of known color data, keyed by symbolic color name (key type:
     * <code>String</code>, value type: <code>org.eclipse.swt.graphics.RGB</code>).
     */
    private Map stringToRGB = new HashMap(7);
    /**