To prevent any disappointment, I would like to say that changing eye color is not possible, as cool as that would be. Belief will not change this. There are simply certain things that are impossible, and changing your DNA with magick is one of them.
However, as stated above, contacts are an option. Also, certain color clothing can change what shade or color the eyes appear to be (red and turquoise shirts, for example, can make blue, gray, or green eyes look bluer).