There was this thing. At least, most of us are hoping it is accurate to use the word "was" because it seemed a rather toxic thing, such that it was easy to look at from the outside and dismiss as LJ Drama, or "a bag full of angry cats" or some other thing that apparently made various people who did not read it choose not to read it and some people congratulate themselves on the wisdom of staying far, far, away.
There are a couple names for it, but the one I've heard most often is RaceFail '09. There is a short summary here, and a linkety guide here including a link to a timeline and another summary of events (she calls it "Writing The Other/Great Cultural Appropriation Debate of DOOM '09" which is more descriptive in some ways, but doesn't have the short quick impression of total morass 'o doom that "RaceFail '09" does). Another comment people should read before diving in, with a lightly shorter link list, is here.
And yes, somewhere in there is evidence that there are certainly people who believe SF (as a written industry, and as a fandom) is not a safe place for people of color. Now, of course, many people will just point at RaceFail '09 itself to prove that point. I don't know how many people will listen to them. I know fandom is certainly both wider and deeper than this particular debate. I also know it is distinctly lacking in characters of color in writing by white people, authors and editors of color in the industry, and fans of color at literary sf cons. There are a few, but not enough.
(apparently there was another discussion last year that was slightly more sane. I remember reading Bear's post on it at the time, but otherwise didn't see much of it. )
If you are going to read any of it, I also recommend you read this essay on the definition of racism and also google "race theory" or "critical race theory" so as to avoid having the "what the heck are you people talking about and why are you mangling this corner of English so no one can talk to each other sensibly on this subject?" reaction in public the first time (like I did).
I have not read it all yet, but I plan to explore further, since the short summary (and other comments I've received) indicate "there have been many interesting and thoughtful posts by fans of color" and those are of interest to me. I hope to post a guide pointing to those later.
In the meantime, one thing some people point to as a positive !fail coming out of this is the creation of a new small press called Verb Noire. They are taking donations now to help them get started.