[Europan Ocean (OP)]

I have heard that animals like dogs and cats see light in shades of blue and yellow. I had as a boy thought they saw in black and white. I have heard snakes see infra red light, but in shades of blue and yellow or yellow and red...? What goes on in their retinas and brains?

[vhfpmr]

Snakes detect IR with their pits, not their eyes, how can we know what that 'looks' like. I'm not sure we even know that two people perceive the same colour in the same way, synaesthetes clearly don't, so I think all bets are off when it comes to a different species. 'Colour' doesn't really have any meaning outside of the visible wavelengths detected by the species who invented the concept.

[Halc]

I have heard that animals like dogs and cats see light in shades of blue and yellow.

Many mammals have cones in their eyes sensitive to these colors, yes. Two is common. I've heard of as many as 16 colors (giving 256 primary colors), but not in a mammal species.

I have heard snakes see infra red light, but in shades of blue and yellow or yellow and red...?

Most snakes are sensitive to green and blue, but some use IR (yes, through the pits) to detect prey.  Mosquitoes and vampire bats have decent IR vision. It's a good thing for a blood sucking species to have. Mosquito's best sense is probably that of CO₂.

What goes on in their retinas and brains?

The retinas are just like any other, but with cones sensitive to different wavelengths than others. As for the brain, one can't say how any of these colors are perceived. Some creature (maybe even another person) might be sensitive to the same colors as you, but perceive them completely differently.

[evan_au]

Understanding what other species experience is the concept of "umwelt": understanding their world.
- But it's hard for humans to understand what would be seen by those women who are tetrachromats (they can see 4 colour bands instead of the usual 3).
See: https://en.wikipedia.org/wiki/Umwelt