I used Mrs Stewart's on Hugo for years. Works pretty well. Takes a while to get really yellow stains out. Fair warning, though...
Be sure to mix the bluing in with your shampoo and don't let it set on the white parts of your dog's coat too long without lathering it up. Don't just squirt it directly on the dog unless you want a tattooed effect. A little goes a long way so just a moderate squirt in the shampoo should work.
It's best to shampoo a small area at a time and then lather. You don't have to rinse it out right away, just lather it up some and squeeze it in before moving to the next area. Otherwise you will have a black and blue dog (think little old ladies with blue hair). The blue does wear off pretty quickly though, should you dye some of his fur accidently. Doesn't hurt the black at all. In fact, I think it deepens it.