Is a Black Hull in the tropics a no-no?

No, I manage a 2007 62' Sunseeker with midnight blue hull (a shade lighter than black). We had it painted with Awlcraft 2000 in 2014 and still looks perfect. Black will show water spots easily.

and salt

Would a black (or dark hull) be much hotter for the interior spaces? I have always thought so but have never owned one. I would expect the machinery space, salon, and spaces under the deck would stay very hot and the AC’s would be run harder than a white hull.

Fiberglass doesn't transmit heat well. So not to a noticeable degree. Not like a steel hull. My concern with black hulls is that they show everything, especially scratches and rubs when the white below shows through.

From our experience, it will be slightly warmer in the Florida sun. The real question is whether it is gelcoat or painted. Dark gelcoat does not last very long here, less than 5 years is what we have seen.

That's a very interesting perspective, and one I haven't seen covered. So basically where a cared for white or light colored gelcoat hull can go indefinitely without having to be painted a dark gelcoat hull can expect to lay out for a paint job in 5 years and every X# of years forever from there. That's something for purchasers of new boats to seriously consider.

The boat I mentioned in midnight blue origionally had gelcoat in that color. I'd have to have it waxed every 3-4 months. At 7 years old, we had to paint it as it was showing through and shot.

What would you estimate as the cost of that paint job?

They look good at a distance, dark colors can get so hot the laminate and fairing can be damaged. A lot of work to maintain a nice appearance.

Absolutely. Fiberglass doesn't transmit heat well, but it absorbs it. So I could see delamination happening. It just won't affect the interior temp as much. Hence fiberglass being used for insulation. I think the OP just got his answer before in #6. The thing he needs to find out is if it's gelcoat or paint so he can gauge his expected future expenses. I've been hearing on here some good things about how long paint is lasting, but nobody wants an expensive surprise a year or three in. Anybody know how much a paint job on a 55 costs these days?

I worked on a 1886 schooner with a black hull in the tropics. Never, ever, have I been so hot.

This from the bloke who puts a hoodie on before his overalls in South America.

My tub is 19 years old, always outdoors in South Florida, and looks brand new.
(After I had the oxidation removed with wet sanding and compounding when I bought it 3 years ago)
Owner of the same make and model with dark hulls had to paint them, even up North.

It was a 62' Predator with a very tall hull, rub rail to waterline is almost 8' I would guess. It was $24k including everything at the time 2014, and that was having a large reputable boat yard in Ft. Lauderdale do it. Hull still looks perfect at 6 1/2 years old and all I've done was have Awlcare wiped on it once a year for $800 including the Awlcare and labor.

Wow, maybe I looked gullible but I got 2 estimates for painting my hull 3 years ago: (I love the New England Navy Blue hull and red bottom paint.)
This was before I had the boat wet sanded and compounded shortly after I bought it, October 2017:
One estimate from Cable was close to $18k, so was an estimate from Patagonia Services, close to $18k.
(28 foot power boat, see picture: www.odincharters.com)

Glad I did not paint the boat, happy with the plain vanilla gelcoat from the factory April 2001.: