Bug 53881 [Colors] Color/Gradient registry should return default values.
There should be default values for when a user does .get() on a bad key.
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);
	
	/**
	 * Runnable that cleans up the manager on disposal of the display.
	 */
	protected Runnable displayRunnable = new Runnable() {