So far no Olympus publications claiming the existence of a black RC have surfaced, and all black ones ever seen either were known and acknowledged repaints or of very questionable origin. The same seems to go for the RD.
In general, none of them are as nicely manual as cameras whose only mode is manual. The SP👎 is the only to have a meter that works in manual mode, but it is uncoupled with only an EV display, and EV transfer to the lens is quite clumsy - if you are mildly far-sighted like me, you might as well use sunny 16 in any lighting conditions where the EV lettering on the lens is reasonably visible. Given that, I'd rate the RC the best manual camera of the three, given the separate time knob on top and a in-finder time and aperture display, even though its meter is disabled in manual mode - even with an external meter it still is much easier and faster to set than the SP. The RD is worst - it has all the weaknesses of both the RC and SP, and none of their strengths.