system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 How do we know which colors different animals see?

Also, would we know if a specific animal had color blindness?
gpt
Dissect their eyes to see the actual color detecting cells and test what light they respond to.

The cone cells have specific proteins tasked with reacting to specific wavelength bands of light, you can expose those proteins to light in the lab and monitor their activity.

Since all animals are at least loosely related, there are only a few variants of these color detection structures and it's pretty easy to see which ones are present and which are missing.