Visual systems and the anatomy of the eye are not the most interesting brain related topic I have read about. The fascinating aspects are more along the lines of philosophical questions, which can almost be answered by science now. Like how do people perceive colour and do they see it differently? I remember discussing the idea that someone might see blue as red with a friend years ago. Is that even possible? Why do children have such a different understanding of colour compared to adults? They paint purple dogs and yellow trees and it seem completely normal to them. Most adults lose this and end up painting things as they appear in their everyday lives. Is it just a matter of imagination, or do our visual systems change over time somehow?
The idea that some humans may have 4 cones and therefore perceive colour very differently is new. It reminds me of a documentary I once saw comparing the colour perception of people living in different habitats. The people living in wet, northern climates could recognise more shades of green than those living in dry, desert climates, for example. Or how generally men and women seem to identify a different number of colour shades. I would be very interested in learning more about the evolution of colour perception and how our eyes adjusted as we transition into moving on two legs. How much did things change when we finally created the first civilizations and cities?
I guess I would say I am more interested in how colour might affect mood or behaviour. The internet is full of generalizations about how differently painted walls may affect the person in the room. Or what the colour of your shirt means. I would like to know how much truth there is to that kind of talk. Can orange/red walls really increase your appetite? Is blue really a calming colour? How does living in a colourful, bright neighbourhood affect you mentally, would it really be better than living in a monotonous area? Is eating multicoloured food better than eating items of similar shades? As you could be eating all green things, all beige things or all brown things during a meal. Purple and blue are rarely seen at meal times. Yellows, oranges and reds are also not present at every meal. Why?