This Anonymous is right. Coloring is just part of a style. Some artists just go solid b/w, I prefer that, actually. Many artists use color as a crutch. A really good artist will be able to show the exact same detail with just black and white. Hell, look at Clone Manga.
And as for this coloring style being the easiest, it's not. The easiest is by far cel shading. Any moron can cel shade.