Guinea pigs’ eyes also have a white sclera like ours, ... So, the coloured part of their eyes is all we can see – it’s usually dark brown, but sometimes it’s blue or even red. Eyes to survive.

P. W. Gregory, Heman L. Ibsen, The Inheritance of Salmon-Eye in Guinea-Pigs, The American Naturalist, Vol. 60, No. 667 (Mar. - Apr., 1926), ... but like the pink-eye gene it has no effect on red hair.