Well, it is not normal for your eyes to change color. And also, it is kind of difficult to identify it. But on the other hand, from your description, I have to say that your eyes may suffer from arcus, which is caused by high cholesterol showing in your eyes. And according to some researches, this kind of eye diseases could occur just as easily as in older folks. For your situation, I will suggest you go to your primary care doctor, and then get a blood test, for high cholesterol is more dangerous for your heart than it is for your eyes. Anyway, just be careful about it.