Colors we haven't even seen

"Oh that's not blue, that's more of a magenta!" My response to comments of this are along the lines of "sure, whatever you say...", but this got me thinking, are there colors out there which humans haven't seen before? Can we even comprehend such an idea (according to some of my friends, we definitely cannot)? Essentially, all shades that are visible to the human eye are based of the rainbow colors, but can we create something out of nothing? Surely individuals in the creative industry would say yes, but in reality, everything we create has SOME reference point, so being able to see something which has never existed in any form... that is just pure crazyness!!