Plastidip never comes out well, imo. If you really really really really need them to be black, then I'd look at powder coating or something professional.
FWIW it does come out well if you do massive prep. Just expect endurance to last as long as your tires last (when you switch sometimes it may get "CHIPPED"/torn if the place is rough with wheels). I go to a touchless place and the plastidip has not come off from them yet. With the exception of amazing amounts of brake dust from track use the color has more or less held up decently but obviously if you are tracking something you don't expect clean wheels lol.