My original idea when Kublai first came along was to give him a greyish colour (Xanadu, looks like the mineral serpentite) and use four bright foreground colours for each of the secondaries. Chinese Kublai would be the direct inversion of those pairs. It didn't end up that way though. I have a feeling with multiple Chinas in-game there will be some truly wacky colour combinations to be had.
I use an amalgam colour for the background of city-states (RGB 64/48/32). I took each secondary colour (like yellow for trade, orange for industrial etc) and worked out the average RGB value of all of them, then picked the inverse colour. It ended up a sort of muddy brown, which I then dropped in brightness a bit to make the secondaries stand out. This freed up black as a primary too, which is a nice bonus.
I wonder if the city names list for China will be extended to account for more playable leaders hailing from there.