It is possible that eyes turn into another color. The color of human eyes is determined by gene. Among all the adults, eye color of part of them will go darker or lighter. It is an abnormal phenomenon of metabolism. Human conjunctiva could be polluted by rays and dust in the air. Pigmentation will occur after a certain period of time and the eye color will change. Scientists believe that original coloring matter of human eyes is melanin. Generally speaking, the amount of melanin is stable throughout the entire life. But certain eye disease and trauma will change that. So, they may result in change of eye color too.
Well, it is normal to have this kind of symptom. So you don not need to worry about it. As we know that exposure to light after birth triggers the production of melanin in the iris of the eye. By three years of age, the eyes produce and store enough melanin to indicate their natural shade. While changes in eye color of infants are more common, even in adults, eye color changes are seen, most often as a result of exposure to the sun. Sunlight triggers melanin production in the eye, as it does to the skin. People with green eyes in the winter might develop darker, more hazel eyes if they spend more time outdoors.