There was a white on black GMK group buy done elsewhere a while back.
The quote we got from GMK for that exact set was a lot cheaper than most GMK buys I've seen. I got the impression perhaps GMK makes some white on black already in their rotation for another customer so they charge a little less for it. Another member and myself were in talks to run something like this but didn't think there would be enough demand.
I know JTK is still in the process of improving and making things better but for the price they are really hard to beat for the price.
Also many cherry doubleshot white on black caps both used and new are still floating around on ebay and here in the classifieds occasionally.