system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 : How are science able to determine what colours animals can and can't see?
gpt
You test the animals.

You teach an animal that if it sees a $ in a pattern of dots, touching it gives a food reward.

Then you put a red $ on a blue card, and see if the animal reacts.  Then a red $ on a green card, then ....

When you look at the pattern of right vs wrong, you know which colors the animal can distinguish.

BTW, this is also how we test for color-blindness in humans, only without the food rewards.