As an African American, I haven't experienced any discrimination as far as I'm concerned. At the undergrad level, my program is extremely diverse and our faculty is pretty diverse as well. Even the grad students are pretty proportionate in numbers. But my program may be the exception.
Just from my acceptances and interviews, I think that I've been given a fair chance and if it had to do with my race, I would not have even had interviews for the programs that are predominately white (which would probably be all except Howard).
But with that being said, in some cases, in may not even be what you know but who you know and I had a pretty good internship in NYC that may have opened doors for me because my GRE scores aren't competitive.
As for HBCUs not admitting POC that often, I find that hard to believe because I keep hearing that we are getting in. And even looking at Facebook pages and such, programs such as Howard's does have mostly POC in them. I mean, it's just a competitive field I guess and they can't admit EVERY POC.