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
Light is an electromagnetic wave. Humans don’t naturally perceive most of the electromagnetic spectrum: https://en.wikipedia.org/wiki/Electromagnetic_spectrum
So, your theoretical primitive alien without technology wouldn’t know, but one with sufficient technology level would know. Assuming that it’s not an ignorant one.