Can bulls see red?

Yes, bulls can see red but they probably can't distinguish it from green. They only have one visual pigment in that part of the spectrum, which means that they can distinguish blue from other colours, but they can't distinguish red from green. They see the world like a red-green colour deficient person. So waving a red rag at a bull isn't a problem because it's red, but because it's moving. They're responding to the movement rather than the red, although they can still see the colour. They will just get confused between red and green rags.