What eye colors can horses have?

Most horses have brown eyes. If lack of skin pigmentation includes the eye, then the eye can be wholly or partly blue (parti-colored eyes are also seen in some species of dogs). This can also lead to heterochromia (one brown eye, one blue).

Blue eyes are also seen on double dilutes. Single dilutes - buckskins and palominos - often still have brown eyes, but they are lighter in color.

The champagne gene turns the eye blue-green at birth and hazel or amber at maturity. Paso Fino horses also carry a gene that produces an amber eye.

Green eyes are extremely rare in horses. They are found in horses that carry the pearl gene (a rare dilute gene) and very, very rarely on homozygous cream or cream and champagne - but in all these instances the eye is more commonly blue, amber, or hazel.

Normal brown eye (source AnemoneProjectors via Wikimedia Commons).

Blue eye on a paint horse (Source: Kalike via Wikimedia Commons).

And a hazel eye. The mottled skin is another clue that this horse is a champagne. (Source AnemoneProjectors via Wikimedia Commons).