So far of all the reds, the plain one is the best. Red clashes with the screenwall and the black chairs. It would work, but I do agree, I'd rather not go plain, but at least I know a color matches out there. The red diamond pattern does match, but over a whole room that pattern would draw all of the attention. A cool carpet can make a plain room look good. A cool room should have a carpet that, in my opinion, doesn't make the rest of the room look bad!
I'm a big hater of any carpet you will see if you google "home theater carpet". Those patterns are just rediculous... like a child's pajamas.
Plain black won't work with black leather chairs, black screenwall.... it will be a washout.
There is another I will show big this weekend. I think it is a discontinued Shaw, because I can find no reference to it anywhere on their site. At this local store though, it is a majority black plush carpet... and not a graphite black or almost black... it's BLACK, and it has small dark gray loop pattern squares inside of it. So at least it is not solid black, but it also is predominantly black.
The black diamond pattern above is not really that black. The dark one is close, but it is still more of a slate. The gray though is what stands out, not the black, and it just appears too light. Then again it is just a small sample. I found a pic of someone who has a very close one and it looks a lot better, when the lighting isn't so bright.
Now look at the same room with NORMAL lighting.