Usually the color of the eyes is fixed which could not change casually. However once it changes, it may indirectly show the problems of the body. You should take notice of it. You need to go to the hospital to have a full check on the eyes. However now you notice a lot of people with hazel eyes turn green. They just wear the colored contact lenses which will change their eyes color to make them look charming and attractive.
It looks like you are very interested in that question. So, generally speaking, the color of our eyes would not change during out lifetime, but some exceptions happen from time to time, that is resulted from some traumas on people's eyes, and consequently, they would get heterochromia iridum, which turns their eye color slightly. What I should say is try to protect your eyes as much as possible.