Do blue-eyed men truly prefer blue-eyed women? And do brown-eyed men really have no preference? As you might expect, this alleged inclination has to do with securing visible proof of paternity: it's rare for two blue-eyed parents to produce a child with a phenotype of brown eyes (though it can happen). A study published in Norway in 2006 says men with blue-eyes do indeed unconsciously seek out women whose irises are lacking melanin, and explains:

A group of 443 young adults of both sexes and different eye colors were asked to report the eye color of their romantic partners. Blue-eyed men were the group with the largest proportion of partners of the same eye color.

According to Bruno Laeng and colleagues, "It is remarkable that blue-eyed men showed such a clear preference for women with the same eye color, given that the present experiment did not request participants to choose prospective sexual mates, but only to provide their aesthetic or attractiveness responses"¦based on face close-up photographs." Blue-eyed men may have unconsciously learned to value a physical trait that can facilitate recognition of own kin.

Makes enough sense. But what of people with aniridia, or people with heterochromia (like Kate Bosworth, David Bowie, and Christopher Walken)? Might have to resort to Level 4 background checks and straight-up pedigree...In the meantime, here's a fun eye color calculator.