Bug 129755 [Decorators] CompositeImageDescriptor: Problem on overlay with transparent areas in PNG
bundles/org.eclipse.jface/src/org/eclipse/jface/resource/CompositeImageDescriptor.java
for (i = 1; i < map.length && (c = map[i]) != null; i++) {
			if (c.red == red && c.green == green && c.blue == blue) {
				return i;
			}
		}
        if (i < map.length - 1) {
            map[i] = new RGB(red, green, blue);
            return i;
        }
        return 0;
    }
    /**
     * Draw the composite images.
     * <p>
     * Subclasses must implement this framework method
     * to paint images within the given bounds using
     * one or more calls to the <code>drawImage</code>
     * framework method.
     * </p>
     *
     * @param width the width
     * @param height the height
     */
    protected abstract void drawCompositeImage(int width, int height);
    /**
     * Draws the given source image data into this composite
     * image at the given position.
     * <p>
     * Call this internal framework method to superimpose another