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
/**
	 * Adds (or replaces) a color to this color registry under the given 
	 * symbolic name.
	 * <p>
	 * A property change event is reported whenever the mapping from a symbolic
	 * name to a color changes. The source of the event is this registry; the
	 * property name is the symbolic color name.
	 * </p>
	 * 
	 * @param symbolicName the symbolic color name
	 * @param colorData an <code>RGB</code> object
	 * @param update - fire a color mapping changed if true. False if this
	 *            method is called from the get method as no setting has
	 *            changed.
	 */
	private void put(String symbolicName, RGB colorData, boolean update) {
		Assert.isNotNull(symbolicName);
		Assert.isNotNull(colorData);
		RGB existing = (RGB) stringToRGB.get(symbolicName);
		if (colorData.equals(existing))
			return;
		Color oldColor = (Color) stringToColor.remove(symbolicName);
		stringToRGB.put(symbolicName, colorData);
		if (update)
			fireMappingChanged(symbolicName, existing, colorData);
		if (oldColor != null)
			staleColors.add(oldColor);
	}	
}