In the company of colors: brand-color associations
filosophy.org
filosophy.org
As a guessing game, I really liked "Unevolved Brands", where logos were reduced to circles and solid colors:
http://www.flickr.com/photos/grahamsblog/sets/72157625155090...
Employees must hate that. How do you get company swag that doesn't look like a harlequin outfit?
There are also some that don't really have color at all. Microsoft seems to just be black on white, even though the Windows brand itself was red, yellow, green and blue.