The closest aesthetic comparison for a glossy black dial is Handwerkskunst Lange 1 Tourbillon from 10 years ago, with the black enamel dial. The onyx dial is clearly a nod to that watch. But of course, enamel has a special quality (in part deriving from the craftsmanship) that onyx lacks. Also, a key feature of the Handwerkskunst dial -- the fact that the "applied" markers are on the same plane as the dial surface (vs. above it) -- is lacking here. But that's unsurprising.
You shouldn't have any regrets, though. The blue dial with the RG case combo is great!!