If you only learn the specific skills you think you need to make a specific thing, you're really pigeon holing yourself. Just because you're interested in this one thing now, doesn't mean either your interest will change/expand or _the expectations _ to do that thing in the industry could change over time.
I would say, if you're just interested in making a free web comic and seeing where it goes, it doesn't matter much. If you want to become a professional artist, you should put effort into having well rounded skills, including coloring.
All that said, if you're a young artist just starting to figure things out, and you're not interested in coloring, it's not like you need to put all your effort into learning that ASAP or anything.