Old, but gold.  


Are the squares A and B the same colour?




Same colour diamonds?


Same colour middles?


These cubes have the same colour faces.


Are the two squares the same colour?


Same colour middles?


Is the central bar a continuous colour?


Are the greens at the sides really that different?


Are the dogs the same colour?


Which square is darker, A or B?


Are all of the greys the same colour? This illusion is known as White's Illusion.


Are the two areas the same colour?


Are the regions marked A the same colour as those marked B? 



Source: http://www.brainbashers.com/showillusion.asp?62

I have seen tests like these. Some of those are or can be the same color because of the angel and or any light or shadow being casted on the objects. This is what can change the color of the object making it an illusion. Those are great thinking illusions though. Thanks for sharing.