To grab attention, colour is better. For someone just casually browsing, coloured comics will naturally make them look, while they might skim over black and white. I've noticed it's the same at cons - people pick up a comic and flip through it, and if it's in black and white, they nearly always put it down again, because they equate colour with being worth more money.
I do my comic in full colour - partly because it grabs attention, partly because it looks nice, and partly because certain elements in my comic require colour to be readable.
I have, however, done comics in black and white - and it's a challenge! You have to plan your layouts and compositions better to avoid confusion for the readers. I did my comics in 100% strict black and white, with no grey tones, which meant I had to work hard so that my panels didn't turn into a mess of lines. Be aware of how and where to place your heavy black areas, where to cross-hatch and where to leave things blank; be aware of linewidth, both in variation (to avoid looking stiff) and in atmospheric perspective - stuff that is further away will have thinner lines, while stuff that is closer to the reader will have thicker lines, etc.
Here's an excerpt of what my black and white comics look(ed) like: these panels don't have a background (and are also, like, 5 years old by now >.<) - but they're a pretty good example of how I used a combination of cross-hatched details and solid blacks to make details stand out.
I inked these with a brushpen on paper, but there's no reason you can't employ the same technique if inking digitally.