Landlord, while you're correct that you can't trademark a specific color for general use, you can trademark it for a specific use, such as on a sports uniform. That's covered here:
http://freakonomics....demark-a-color/
From what I understand, Nike has a trademark on the color "maize" for use in athletic uniforms, so Michigan had to switch to the color "sun" when they switched to adidas. From what any of us can tell, the two colors look basically the same, but Michigan fans insist they're different and they are technically different colors.
If Michigan or adidas really wanted to, they could probably take Nike to court for use of the maize color, but it's not really worth the time or money for something as trivial as that.