Actually staring at the sun will not make your eye color look lighter. It is from the visual side that your eyes look lighter because of the bright light's shining. The color of the eyes is fixed based on the genetic endowment. Once it is changed, you'd better check whether there is the problem with your body.
Lolo..., you are so strong. You can stare at the sun? It seems impossible. Most of people can't open their eyes to stare at the sun unless they wear sunglasses. Anyway, as far as i know, stare at the sun won't make your eye color lighter. The color of the eye is decided by gene. And there is no other way to change it. If you want to make your eyes look brighter, you'd better take more vitamine C. Hope this can help you.
Oh, why'd you think that? I don't understand your idea actually. So, as a matter of fact, the color of your eyes is primarily decided by your gene type, which has nothing to do with light or something. And by staring at the sun for much too long, you are likely to get a poorer vision, damaged eyes, even get blind forever. So do not try to do anything stupid and take care of your eye health.