I was just about to start a similar topic, till I read yours.
Black people are awful on this show, as they have little to no knowledge of a lot of topics outside of hip hop music or some sports.
I have been watching this show everyday for about 8 months and I honestly can't remember if black contestants have ever won the $20k.

You haven't seen very much of the show then because contestant or celebrity ability has been all over the place and covered the full spectrum of very bad to excellent no different than the white contestants. From what little you have seen, you don't seem to have a very intelligent grasp of how the show works. Charades has nothing to do with the show, in fact, it's actually the opposite of charades and word association would be more descriptive. To use charades to describe the show makes you more of a dumbass than anybody I've seen appear on the show.
Victory is Mine!!!

I've noticed this also,but especially with the celebrities

They don't seem to know much of anything that doesn't relate to their own race. Answer-joan of arc. Clue-queen. She was beheaded. Answer-scientology. Clue-a college course

This game show has nothing to do with charades, it's a word association game.

The sun is shining but the ice is slippery.

No, some have done well, and some of the celebrities have been very good.
There may be a bit of a cultural thing going.
There was one episode where the white couple got to the last round with something like $2300 to $500 but the topic was 'rappers' (it may as well have been 'stuff only black people could possibly know') and the black couple won the game but did terrible on the final set. I would feel seriously robbed if I were that couple. Categories should not be so one sided especially for that final round.
On the other hand though, I suspect many of the other categories would have a slight tendency to work in favour of white americans, though it depends on how out of touch they are with regular american culture. There are only a few categories I have seen where the difference is massivesadly one of those is Rappers.