I think we're talking ablout two different construction methods...
"Gelcoat" generally implies female mold, fiberglass laminate
construction with polyester resins, where the colored gelcoat is
applied against a release agent, (preventing the gelcoat from sticking
to the mold) followed by a few to many-many layers of fiberglass of
various weaves & thickness. Here, the 'color' is the *first* item to
be applied (against the female mold).

"Paint" is generally used in male mold construction, mostly used in
"one-off" boat building. (Paint is also used over "old gelcoat" after
it has faded after years of sun/abuse/neglect). In M-M construction,
various materials (cold-molded wood, sheet "foam", fiberglass planking)
are laid over a male mold with the hull thickness then laminated up
(often using epoxy resins) with either additional wood veniers, woven
or knitted fiberglass, kevlar, carbon fiber or what-have-you.
Here, the paint (color) is applied *last*, against a primer that acts
as an adhesion base for the paint as well as a barrier against any
epoxy 'blush'.

As to the weight: One applies Polyurethane paint in multiple (like 3)
*very* thin coats. I'd guess you could do a canoe with about a quart
of paint / solvent / reducer which might weigh (guessing) about 2 lbs
(total).

MW
Los Angeles