Afaik those darker skin tones & additional hairstyles where added later to the game and do not appear with randomized characters. So you are right.
Ofc it would be nice to have the option for more skintones & more hairstyles for random characters. Both should be seperately optional because: especially some of the hairstyles are very uncommon / unnatural.
Would love to see a haridresser in town where you can change the hairstyles of all characters, if they agree.
Skin tone change would also be cool, like getting a tan on the bech or in a human toaster - tan should ofc fade with time. Imho "tanned" should not be its own skintone but a condition.
regards,