I wondered the exact same thing about colours as a kid. I'm still not sure the answer

I don't know about reality. I guess it's usually based on the consensus view of what is happening, so if enough people agree on something it must be real. I used to do a lot of hallucinogenic drugs when I was a teenager, and I thought about the concept of reality a lot. If I experience something, it is real to me, even if others don't experience it or agree. I had a few pretty terrifying experiences of loosing touch with consensus reality. I'm still not sure how to make sense of those kind of experiences, because I wonder if I was just able to tap into some other level of consciousness that is usually imperceptible or if it was purely psychosis.

Interesting topic