I have a thermometer I put under the cover in the spring. It has a 2nd sensor I put in the engine compartment & it records max high & low temps. I've seen over 150 degrees in the spring when the sun is shining & it's maybe 60 or 70 degrees outside.
When I pull the cover off the boat in the summer it takes a few minutes for the interior to cool down.
I have an all black cover and a mostly black boat and no real problems with heat.Once the cover is off it cools down fast.My issue with the black is the damn water spots on the gel.Black gel coat looks great,but is a pain to keep that way.
The only thing is being in Georgia is the humidity. If your leaving the boat outside..... with the heat... it's going to harbor a lot of the humidity. I would just think it wouldn't be good for electrical connections and such.
It's unreal how hot it gets, and I have actually been burned in august when I have climbed into a black cover. Also remember that the snaps on your cover will become EXTREMELY hot. It takes more than 30 seconds to cool off if it's a 100 degree+ day.