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
public void run() {
			clearCaches();
		}
	};
	/**
	 * Create a new instance of the receiver that is hooked to the current 
	 * display.
	 * 
	 * @see org.eclipse.swt.widgets.Display#getCurrent()
	 */
	public ColorRegistry() {
		this(Display.getCurrent());
	}
	/**
	 * Create a new instance of the receiver.
	 * 
	 * @param display the <code>Display</code> to hook into.
	 */
	public ColorRegistry(Display display) {
		Assert.isNotNull(display);
		this.display = display;
		hookDisplayDispose();
	}
	
	/**
	 * Create a new <code>Color</code> on the receivers <code>Display</code>.
	 * 
	 * @param symbolicName the symbolic color name.
	 * @param rgb the <code>RGB</code> data for the color.
	 * @return the new <code>Color</code> object.