OK, so googling Buckeyes came up with some nice deep red photos. Oddly, it also gave me a chart of chicken breeds that said Buckeyes only come in nut brown. Just goes to show you can't believe everything you read on the internet!
The dark Cornish search didn't mention their actual color, but I found photos of what look like black chickens, so I'm guessing that was just the lighting, and they must be really dark red, like Fred's photos of the RIRs.
I'm new to chickens and haven't really dug into their color genetics yet, like I have with my parrot species. But I'm getting the impression that the wild type coloration is in some breeds called "partridge". And that can sometimes look reddish. Do I have that right? There must be several breeds that come in that color.
It would be really great if more people would put up some photos of their other types of red chickens.