So let’s say this Alien eyes see on the infrared level, he would see normal RGB like you and I, but could be still know there is colors there? What reason is there for the alien to discover there is colors there?
I think I can’t imagine how we discover something that we don’t see, or mostly that there is something that I don’t know
If they evolved to perceive certain wavelengths, they will see those wavelengths. The wavelengths that they haven’t evolved to see could be observed using specialized tech.