I had thread on another forum about deer vision. I did some research and discovered deer have quite good colour vision. They are dichromatic as opposed to humans being trichromatic. We have blue, green and red colour cones in our eyes as well as monochrome rods. Deer have rods as well as blue and green colour cones. But, they have very large irises which let in a lot of light so they see well in starlight. Another difference between theirs and ours eyes is we have a yellow pigment in out eyes which filters out UV, they don't. They don't see the colour purple like we do. They see it as blue just like UV. Purple is a composite of red and blue and we see it because our red cones have a sensitivity at the near ultraviolet so we see a mix of blue and red = purple.
It has been said that deer see some yellow in a shades of grey world. They don't. They see greens and blues and a mix of those colours (although we have no idea how their brains actually perceive colours) in a coloured world just like we do but what we see as white would be cyan to them (their equivalent of white, which could well be their white).
They do see UV in low light and possibly in bright light too. The significance of that is the washing powders we use to wash our cammo gear!
Deer do not have the visual acuity that we do. What they see is possibly like what wee see in our near peripheral vision, say about five degrees off central vision.
Deer also do not see light in the far red, which is out of range of both their rods and green cones. That has little significance for us though but we could theoretically stalk them in the dark using a deep red light. Trouble is we don't have good vision in the deep red anyway and besides, we don't hunt at night unless on private land.
P.S. Turkey see six colours! They have four colour cones, two of those have colour filters, giving them the six colour receptors.
