[rodeo02]

Some motor oils darken up quicker than others. Dark does not mean much. Fuel adds can work their way into the oil in trace amounts, but you'd only see it by getting an analysis done on the used oil. For the $20-30 that would cost you, you are better off just doing another oil change. The only time I'd worry about the color or the oil, is if it were light brown, milky, foamy, or thinned out & smelling strongly of gasoline. Those would indicate problems with the engine. New oil in a diesel turns BLACK in just a few hundred miles. Just check your oil weekly & change it out with a schedule that works for you. I do mine about every 4000 miles with regular old 5w-30 or 10w-30 (usually havoline, napa, or carquest oil & filters). Equates to about 4 oil changes a year.
G/luck
Joel