Actually RP accepts quite a bit of B&W, both the real stuff and the digital version.
As best as I can tell most of the screeners at RP are on the younger side, and their experience is entirely with digital. Occasionally I will get a rejection for "noise, the digital equivalent of grain". So I appeal along the lines of, hey guys this ain't noise, this is a 40 years old slide and this is real genuine grain. Live with it. Then it usually gets accepted. The standards are quite age related...older stuff can be technically pretty poor if the subject matter is interesting.
RP seems to have started out as something of a roster shot kind of by the engine number gallery. But it really has evolved, and several of us who post there regularly keep challenging the limits. We've made progress, it's fun, and I really do think there is some good stuff there.
That said, variety is the spice of life, so I'm always looking for new and different places to post. "Deviant Art" sounds like my kind of place. But my favorite is simply my own website, where I have full control, for better or worse:
Narrow Gauge Memories
John