Take a look at this picture...

The spots are all white

This is what is called an "optical illusion" and it is a picture that makes you think that you are seeing things that are not really there. It is your brain that is being tricked! It happens because of the way that your eyes see light and dark colours and edges of shapes. In this picture, the spots seem like they are changing colour from black to white, but it depends where your eye is looking at the time.