Red is light at the 480 THz range. Blue is light at the 670 THz range. I think that's perfectly described using terms of the physical world. If you're talking about "what we experience as color" as being difficult to describe in our consciousness, then sure but that's the case for every single thing we experience. Same way I can describe the musical note A as 440 Hz. Does an A to you sound the same to me? My tongue is sensing a sugar molecule, does the experience of tasting it feel the same to you?

Not a single human perception can be described in words, but we can all compare perceptions to other perceptions and agree on the same answer. Perceptions are simply us recognizing patterns in our environment. Red is me recognizing my eyeball is looking at an object reflecting light in the 480 THz range. You look at that red ball and you also recognize it as reflecting light at 480 THz. Does it need to be described any further?

It all exists in some capacity. Color is either the electromagnetic frequency emitted by particles when stimulated by radiation, or it is the electrochemical signals firing through your brain which process an image based on the way cells in your eyes absorb those frequencies. Or, more precisely I suppose, the intersection of both is where "color" exists, as one cannot occur without the other.