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> > To be precise, phylogenetic bracketing: It's normal for vertebrates to
> > have 4 types of cones in the retina, for red, green, blue and
> > ultraviolet.
> Interestingly, humans don't have a red receptor. They have an orange
> one, and use it to interpolate what red should look like. So every time
> you look at something red, the colour you see is not the "real" colour,
> but your brain's idea of a "best guess".
Which is what I mean. It's commonly called "red". AFAIK it's more yellow
than orange (the reddest of the three, anyway), and IIRC 32 % of people have
an additional 4th one that is more orange -- yet another gene duplication?
> I think this is due to the fact that green vegetation reflect very
> strongly in the near infrared, hence if we could see in those
> wavelengths we'd be practically blinded everytime we went outside.
> Perhaps the lack of a true red receptor is due to the eye's evolution
> trying to avoid the near infrared, and creating a buffer zone around
> those wavelengths?
Sounds interesting. Does anyone know how "red" the plesiomorphic "red"
receptor of vertebrates is?