the general color of the Wire even with tinning, might not be that bright though.
I know that once you alloy copper, it begins losing it's conductivity and when you bring it to brass or bronze, it's down quite a bit.
I don't know if it's feasible to make Wire out of alloy that costs less, by adding zinc or lead or some other silvery looking metal to copper, based on how much all those added metals cost.
I believe it's possible to source out cheaper wire in Chinese factories, where you don't know how pure the copper is and if someone like KnuConcepts, were to take advantage of that fact, and nobody ever assays the copper in the wire they are selling, they could be making up the short end price-wise, by using less than pure copper.
Generally, Car audio might not be an authority, there is probably no CEA-2006 spec that regulates wire and the metal content found in it, so if the wire appears brighter than pure copper, it might be just that.
I know copper does tarnish and it's usually quite bright, and not all that red, or pink for that matter.
But when you cut into a tinned copper wire that claims "OFC" then it shouldn't have tinning at all, it should be pure in my opinion.
after all, OFC just stands for Oxygen Free Copper, which doesn't really mean Oxidation free either.
and Copper doesn't rust, it corrodes and tin is more inert, not going to corrode in normal atmosphere.
After seeing copper wire turn green inside it's clear plastic jacket, I think tinned copper is better for any purpose, not just marine environments.