i think its silly to determine the condition of the oil by looking at the color/shade of the oil. in most cars, oil will turn black after 500 or so. the best way to determine oil life in an engine is to analysis it, and the ultimate numbers that everyone should care about is the metal wear residue suspend in the oil. if you take your oil to 7k, and it shows little engine wear in the analysis, that should pretty much conclude that the oil is safe to go to that length. changing your oil at every 3k is a waste of money and harm to the enviroment. it only benefits the dealers, quicklube, and the oil companies.
you guys should really check out this forum and learn everything about oil:
http://theoildrop.server101.com/cgi/ultimatebb.cgi