as for "real world differences" there are none save the fact that different crystals are used. the color only depends on the type and size of crystal used. Blade lenght depends on the size and number of crystals used, some of the ancient Jedi masters had blades that could extend due to a multi-crystal design. Each additional crystal seems to give the saber about 3 feet of additional length, thus a 3 crystal lightsaber can go (on average) to 3 meters or about 9 feet.
yes, I do realize this lables me as a SW freak, but the truth was bound to come out sometime
-spike