: Just pigmented epoxy will have at best mild resistance to UV.

Depending on the amount and type of pigment, it can actually be quite resistant to UV, but it won't be as good as gelcoat or paint.

: The reason for gelcoat is primarily to make it easy to get the boats out of
: the molds and to protect those expensive molds.

The reason for gelcoat is to provide a sacrificial protective layer for the boat that is high gloss without the need to buff the surface after it comes out of the mold. It has nothing to do with protecting the molds themselves.

: Now days paint is much better.

It's probably his best solution. A good hull paint will be durable and easy to repair. It's also easy to apply.

: Pigmented resin "might" give you a white hull but it'll be tinted somewhat
: amber because of the color of the resin.

More importantly, you won't achieve an opaque color unless you apply it quite thick. Additionally, epoxy tends to run unless you thicken it, but thickening it reduces its ability to self-level. It will probably require extensive sanding and buffing to get it level and smooth.

My advice would be to paint it.