“Julie hated pink. It also seemed as if she could discern gradations of red on the electromagnetic spectrum that no one else could. Humans are ‘trichromats,’ meaning we have three different types of cone cells in our eyes. However, it has been surmised that because of the XX chromosome, some women may possess a fourth variant cone cell, situated between the standard red and green cones. This would make them — like birds — ‘tetrachromats.’ These hypothetical tetrachromats would have the ability to distinguish between two colors a trichchromat would call identical.
“To date, only a few female candidates for tetrachomacy have been identified. I didn’t tell Julie my suspicions. And I’m not saying she is a tetrachromat. But it sure would explain several of those extra hours in Tech, when Julie had hues finessed to a fare-thee-well. But then again, a writer will fuss over a single word, to the exasperation of a choreographer who will make endless refinements to a dance step, deliberating between differences an engineer can’t even perceive. In other words, an obsession over subtleties may just be an attribute of expertise, rather than evidence of being a mutant. Still, a scientist should check her out.
— Glen Berger, Song of Spider-Man: The Inside Story of the Most Controversial Musical in Broadway History, pp. 146-7.