I heard that some people's eye color will change according to the light. If they are in a more lighted place, their eyes will turn a light green. If they are in a more darkness place, their eyes will turn a more brown. Doctor thinks that some people's eye color do change naturally in a long due process, it will take them almost decands of years. Usually this will not happen in one night.
You can ask you mum to take your sister to see the health care practitioner. If the gene alteration occurs in the cells of your iris, you color of the eyes will change. If our body is exposed to UV rays for a long time, the melanin production in the iris will increases. Then the color of our eyes may change. To some people, their eye color will change according to light refraction and emotions.