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
We routinely take photos in other frequency ranges. It’s easy enough to find infrared photographs, made easier since not only is there film that exposes IR, but digital cameras are naturally sensitive to it so you just need to change out some filters. But you know, astrophotography often uses different frequency ranges, since a lot of stellar phenomena emit different kinds of radiation.
The bigger question is, would an alien without eyes at all be aware of electromagnetic radiation? And conversely, what phenomena are there that would be obvious to aliens but we just don’t know about, because out sensory organs don’t predispose us to being aware of them?