Generally, eyes should be circular.

Pupils

As a general rule, eyes should have a round dark pupil unless they have a mutation or unpassable trait that states otherwise.

• Pupils don't have to be black, but should be quite dark.
• Pupils don't have to be perfectly circular, but should be round.

Mutant eye colors

Some pigment mutations change the eye color.

• Albinism (al), Piebaldism (Pb, if it covers an eye) and Xanthism (xa): Turns the eye red, purple or blue, with a lighter pupil. This will also detract 1 PER for each eye affected.
• Double Roan (RN): Turns the eye light blue, purple or red with a pupil of a midtone shade of that color. (Basically the albinism rules but in pastel instead) This will detract 2 PER.
• Axanthism (ax): Turns the eye dark brown or dark grey.
• Iridism (ir): Turns the eye a bright color and the pupil white. Aniridism (ar) does something similar, except the eye is a dark color and the pupil is a bright color.

All other pigment mutations (Melanism, Leucism, Clear Body, Erythrism, Dilute, Concentrate) do not change the eye color. Normal phonies can have their irises be red, blue, brown or purple, but with these mutations, the iris has to be those colors, and for al, Pb and xa, the pupil gets to be lighter than normally acceptable.

Heterochromia

Phonies cannot have sectoral heterochromia. You may include a band of luminous color on the phony's eye as long as they're similar colors. Phonies with piebaldism covering part of their eye may bypass this and have the eye be partially affected. Phonies may have complete heterochromia.

If you have the "Even Weirder Goop" item, purchasable in the event shop during the halloween event, you can bypass all of these things and give your phony completely unique eyes. This awards an unpassable "unique eyes" trait that lets you go ham. The only stipulation is that the eye itself should remain circular. Other than that, go wild.