It is possible to change eye color. I heard that eye color can be changed drastically with the first six years of life. After that, you can seldom change your eye color. Usually, most of color changes happen during parts of your life. For example, your hormones are in flux, such as puberty or pregnancy etc. And the eyes will change color slightly as you age. If there are noticeable change in your eye color, it often a signs of an underlying health problem.
For most people, the eye colors were formed early in our childhood, and wouldn't be changed except for injuries or gene variation, because the eye color is determined by the melanin density of iris, which is also determined by the differentiation of relative genes. According to a scientific research in 1997, thousands of twins were studied and came to the conclusion that the eye colors of 10%~15% of the twins had a continual change from their adolescence on. This also proved a fact, that the genes determining the eye color of the twins are the same and conduct the same differentiation process.