Men are red, women are green.

Here is a curious bit which I pass on from the Random Samples section of the Dec. 19 Science Magazine, describing the work of researchers at Brown University:

Men are colored like Mars, but women are greenish--and the difference may help explain how people perceive la difference...Cognitive scientist Michael Tarr and grad student Adrian Nestor made the discovery by averaging mug shots of 200 white males and females into a single androgynous face. They then obscured it further with randomly placed red and green pixels.

Three volunteers looked at 20,000 different versions of the image--some redder, others greener--and told the researchers which sex they thought each face represented. The result: Faces with green pixels were tagged as female and those with more red pixels as male. The color of the cheekbones, nose, and sides of the mouth were particularly important to decisions, says Tarr, whose paper is in press in Psychological Science.

Marlene Behrmann, a psychologist at Carnegie Mellon University in Pittsburgh, Pennsylvania, says the fact that people subconsciously recognize the red-green distinction "means there is something evolutionarily and ecologically important about color that extends even into the human central nervous system."