I colored the first chapter for my comic, which got me a good amount of followers right from the start. (I uploaded the entire thing in one go) But now I've moved on to greytones, and I've not received a single complaint from my readers.
I've had people unsubscribe after a while, but the reason could be anything.
Colors looks nice and all, and it makes comics usually more pleasant to look at. However, I personally wish people weren't that obsessed with colors. There are so many comics that define their characters by what colors their hair is etc, instead of defining them by body types and such. With black and white/greytones you're forced to be more creative with your character designs.