Although you will find that your eyes' color in the sun is lightened under the strong sunlight, the actual color remains the same. This is because of the visual side. When the color of the eyes changes, you must have something wrong with your health. You need to pay attention. In addition, you should not expose your eyes under the sun for a long time which will be damaged at the surface.
Ok, truly, with the exposure to your eyes to sunshine, it would make your eyes look brighter, but that is temporary and natural, in essence, the color of your eyes actually do not change. And by exposing your eyes to sunshine for much too long, your eyes are likely to get burnt and even lose vision permanently on a forever basis, just take care of your eyes and do not try anything stupid.
It is not possible for people to change the color of eyes when they expose eyes in the sun. The color of eyes is born to be as they are. And there are many ultraviolet rays which are harmful to the eyes in the sunshine. So if people just watch the sun straight, their eyes will get hurt. To be more serious, their eyes may get blindness. To change the color of the eyes, you can just wear cosmetic contact lenses.