Stained Glass Illusion
What to see and do:The colors should seem pretty bright at the beginning, but when you move the black outer frame, the colors should seem a little more bleak and dull.
What's happening: Colors usually seem brighter when they have a backround. Black lines are the most common color used to enhance the brightness of colors.
Credit: This illusion is based on an illusion at http://www.personal.kent.edu/~rmuhamma/OpticalIllusion/illusion.html