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
Color color = createColor(symbolicName, (RGB) result);
		if (color != null)
			stringToColor.put(symbolicName, color);
		return color;
	}
	
	/* (non-Javadoc)
	 * @see org.eclipse.jface.resource.ResourceRegistry#getKeySet()
	 */	
	public Set getKeySet() {	    
	    return Collections.unmodifiableSet(stringToRGB.keySet());
	}
	/**
	 * Returns the color data associated with the given symbolic color name.
	 *
	 * @param symbolicName symbolic color name.
	 * @return the <code>RGB</code> data.
	 */
	public RGB getRGB(String symbolicName) {
		Assert.isNotNull(symbolicName);
		return (RGB) stringToRGB.get(symbolicName);
	}
	/* (non-Javadoc)
	 * @see org.eclipse.jface.resource.ResourceRegistry#clearCaches()
	 */
	protected void clearCaches() {
		disposeColors(stringToColor.values().iterator());
		disposeColors(staleColors.iterator());