What we see is determined by the visual pigments of the human eye. We have often asked what our dog might see. Colour vision was thought restricted to the primates. Totally wrong. Thanks to a paper by Justin Marshall & Kentaro Arikawa in Current Biology we know now that colour vision is very common in the animal kingdom. There are several species that use a much broader spectrum to look at their surroundings. Honey bees for example can identify objects in the UV part of the spectrum. They have, however, three different photoreceptors like humans. Waterflees or the Blue Tit have four different ones the former sensing the whole spectrum from 300 nm to 700 nm. The latter misses some light in the infrared part. Horses and dogs have only two different photoreceptors, they are in way green–red blind. Dogs, however, have a much more discriminating capacity in the dark.

What comes as a surprise is that butterflies and other insects can differentiate the visual reception with up to 8 different photoreceptors. And this is not the end: Shrimps have 20: (cited from the paper)”Twenty receptor types have been defined: twelve for colour, six for polarisation and two with overlapping function for luminance tasks”.

An eye-opener. Nice and Recommende!