Eye color is based on pigment coloration.
Changes (lightening or darkening) of eye color during early childhood, puberty, pregnancy, and sometimes after serious trauma (like heterochromia) suggest that eyes sometimes change color under certain circumstances, due to chemical reactions or hormonal changes within the body
 Under the same environmental conditions, there may be disagreement over the color of an object between two different people; the factor that causes this discrepancy is the presence of melanin in the iris, which is the main factor in determining eye color

