Woolite For Darks. Cleans ok and smells great. We use it in a top loader with lots of water, results in front loaders might not be as good.
Sometimes what looks like color fading is actually an accumulation of optical brighteners, liquid detergents, fabric softener waxes and assorted other crap. If you have or can get a top loader, Charlie's Laundry Powder is excellent at removing these residues.