If this phenomenon just happened in sunlight, there is nothing to be worried as far as i am concerned. It is a quite a normal situation owing to the light reflection. When your eyes are in sunlight, a light beam will enter into your eyes, part of the light is absorbed by the eyes, and part of the light is reflected out, cause the retina is just like a minute surface. Therefore, you can see this interesting phenomenon, changing color of your eyes. But in fact, your eye color does not change at all. This is just a kind of optical phenomenon. And you do not need to worry about it. However, if you have some discomfort in your eyes, you must go to hospital for a detail eye check.