Agree with you on your last observation Keith. A weeks review of variation/error listings on ebay will prove that point.
But some color variations are fairly dramatic...the 84 blueless being one example. Also take a look at the just completed listings for1984 "Topps blackless Encased" cards on ebay .
Doug on here has a 58 Aaron where the background is blue rather than green and I have Mays from 1966 with blue versus green banners.They are both pretty dramatic. My Mays may just be green faded to blue from sun or light.
I guess if you wanted to create some dramatic color variants you could just leave some cards in a sun facing window sill for 6 months