You know there are colors from red to violet, right? even when you see in ultraviolet, infrared or x-ray; you will just see any of the existent colors regardless of whatever wave you are seeing through. but what if there was another color off the spectrum (i mean a color which doesn't exist, something impossible, not the ones we can't see). if there is another color, then it should be intangible to our perception and dimension..
Color is just the word we use to describe how our brain processes certain wavelengths of light. Asking if there is another color outside the visible spectrum is kind of moot because it's not part of the visible spectrum - our eyes don't pick up those wavelengths.
Reindeer are one of the only mammals that can see ultraviolet light. They use it to detect food, predators, and traces of piss in the snow. It's possible that from their perspective, ultraviolet light corresponds to a color none of us know about, but that's just because they interpret it that way. There's nothing about ultraviolet light that makes it 'colored'.
