When I type "red cow" into google translate it gives bó rua, but when I just type red it gives dearg

What's going on here? Thanks yall!

Rua is generally used when referring to hair or an animal's coat, while "dearg" is typically used in conjunction with more artificial occurrences of red. A red haired person is often described as rua. Similarly, with animals, a madra rua (lit. red dog) is a fox. This might be compared to the distinction between "ginger" and "red" in English, though "ginger" would hardly be used to describe an animal in English as rua is in Irish. I suspect google translate has learned this context and interpreted your "red cow" as being "a cow with red fur" as opposed to "a cow painted red".

It should also be noted that colours often don't match up precisely between languages. Often slightly different shades of one colour in one language constitute two distinct colours in the vocabulary of another language.