Pretty tough to do and it will scratch off easily, however it can be done. You will need a big bottle of heptane ( bestest rubber cement thinner available at Home Depot in the paint department). Depending on your top coat color you will need a base coat of something to create the bonding layer (I would use white if it's going to be a lighter color). You will need to do small areas. Basically tak a clean rag and soak it with the heptane then lay it over the area you plan to paint, keeping it wet and allowing the heptane to disolve and soften the surface, it will need to soak for a few minutes. Take the rag off and wipe the area dry (must be done quickly), now spray a thin coat of Krylon for plastics spray paint over the area (not too thick, and coverage doesn't need to be 100%).
Move to the next section and repeat until the whole hull is sprayed, let it dry, then spray with your final color, if you can find the right colors with the Krylon plastic spray, great, use that. Otherwise use whatever paint you can find with a similar base (so it doesn't curdle). If you want black, that truck bed paint works well but give you a Kringle finish.
Once everything looks the way you like it, go over a couple more times with clear coat ( that Krylon for plastics clear coat bonds fairly well to plastics.
If your trying to do a camo job on the boat this might be ok, but if your just wanting a different color boat, sell this one and buy the color you really want, it still valuable if not painted, and most Hobies in good shape sell for 80% of new price, once you paint it, it won't be worth anything (just so you know)
Hope this helps