Eye color is determined by the amount and type of melanin in the iris. Melanin is a pigment that gives color to the skin, hair, and eyes. People with more melanin have darker eyes, while those with less melanin have lighter eyes. The amount and type of melanin in the iris can change over time, which can cause a person's eye color to change. For example, some people's eyes may get lighter as they get older, while others' eyes may get darker. However, eye color is not a chemical change because the chemical composition of the melanin in the iris does not change.