Nu-Image is good, I've used it and my "hard to get dappled up" horse got 3 dapples on each side... needless to say I was ecstatic.
This year I'm just doing a very good Hoof Supplement and it has Omega 3 and Omega 6 in it and his coat has really bloomed.
The only problem with Black As Knight is if you plan to compete you have to pull them off of it a good amount of time before the show. They use paprika which causes the drastic change in the coat (frankly you can do it cheaper by just buying the paprika in bulk). But paprika tests positive when they are drug tested at shows as Capcasin. So be careful!
Gordon Wright once told a student to take up swimming because he would never be a good rider, that rider was George Morris.