The primary causes for change in eye color include advancement in age and change in pupil size, according to All About Vision. Eye colors may also be changed through the use of contact lenses or cosmetic iris implants. Certain rare diseases also cause dramatic shifts in color.
Approximately 10 to 15 percent of individuals of Caucasian descent experience a change in eye color, generally from darker to lighter, as they age, reports All About Vision. Additionally, certain emotions or changes in brightness cause the pupil to contract, forcing the colors of the iris to become more enhanced. This is the reason that some individuals seem to exhibit changes in eye color when they are angry or loving. Sudden changes in eye color can also be caused by Fuch's heterochromic iridocyclitis, Horner's syndrome or pigmentary glaucoma and should be treated as an early warning sign.