There are three main differences between black bear and grizz. Ears (short and round for grizz, longer and more pointed for black); face (dished for griz, flat for black); the grizzly hump (note that in some positions black bears may appear to have a hump). Normally all three features are required for positive identification. Coat color is definitely not a distinguishing feature. "Black" bears come in a variety of colors from black to brown to cinnamon to blond. Grizz also vary in color, although not as much.

Here's an excellent program for learning to tell the two species apart: Montana Fish and Wildlife Bear Identification Program. Click on "Start training." It's the training and test required for Montana bear hunters. There are some "borderline" photos there that will challenge you!