Red hair was sexually selected

We recently had a debate as to which animals have colour vision. Being avid fly fishermen, we debated wether the colour of the fly really does anything. Can fish see colour? Obviously tropical fish are very colourful but can they appreciate it? Well it turns out, that fish may in fact see more colours than we do. Some of them can see ultraviolet as well as infrared. In fact if you look at reef fish with a UV filter, all kinds of new interesting patterns emerge. The goldfish for example has 4 different cones sensitive to different wavelengths. This brings up the question as to why evolution drives the selection for colour vision. Our ability to see red, green and blue is actually a recent event in our common ancestors with primates. The proposed hypothesis for the evolution of red vision is that it enabled the foraging of ripe fruits in the green background of the vegetation. From then on, red hair, and red appendages were positively selected for in primates by sexual selection. Red hair effectively became sexually desirable, and a red bottom for example, would be a very good cue of the receptivity of the female monkey.