As stated, gelcoat is a different animal. If you were looking to do a proper job re-gelcoating a new color over the entire boat it could get quite expensive, possible in excess of the value of the boat in totality. That said, I've seen people repaint the top of a boat (say rub rail up) with varying degrees of success.
Paint on a boat is not like paint on a car, and for good reason. It's much more scratch, ding, scuff, and wear resistant. Most people don't climb all over the top of their car on a regular basis...if they did, cars would probably be gelcoated.
The good news, I've seen terribly old, incredibly faded (nasty) gelcoat returned to near showroom condition...if you can tolerate the factory color. Gelcoat is very resilient. My last boat was a neglected '83 Glastron-Carlson...after a couple days with a buffer, the hull could pass for a new boat.
Me personally, if I felt the need to drastically change the appearance of my boat...I would look into decals (or boat wraps) before I'd think about repainting it. 2 cents.