I think it all depends on how much time you're willing to devote to the comic and what you're going for as far as visual style; do you have the time to devote to a color comic or would that just stress you out inordinately? Would coloring the comic make you much less inclined to work on it? Would color detract from the content and presentation of the comic itself?
One of my comics is very simple black-and-white because they're just small, funny gag comics that don't need a lot of polish, and I like being able to sit down and churn out a handful of them every time I feel like cartooning. Occasionally I'll add a single color to individual comics, but only if it enhances the line work or I want to make some sort of visual impact (for example, the rare occasions where the comic has a background, or when I want to portray a shadowed subject in the extreme foreground). On the other hand, I flat-color my other comic, but that only updates two pages a week so I can devote a little more time to giving it color; that, and black-and-white comics tend to give my writer a headache so she requested when we started that I draw the comic in color.
So yeah, take it on a case-by-case basis. If you want to experiment with color, go for it (art is all about experimentation), but if it's not working for you, don't be afraid to go back to B&W.