Rolf,
I built a black boat and sailed it for 13 years.
The deck does get hot but all you have to do before you start is put your hand in the water and bring it up with some water in it and splash it over the deck. It's no big deal.
Once you're underway more often than not water is splashing up on the deck anyway.
The only real issue to consider is the breakdown temp of the resin used.
And believe it of not "resins ain't resins". They can vary a lot.
You can't compare a high temp re-preg resin like that used to make carbon masts to a normal resin used in boat constructoion.

I kept my black boat under cover until I needed the covered area to build a big boat. Then I moved out into the direct sun. Several years later the decks started to delaminated. It was the glue holding the layers of veneer in the play that gave out.
If the boat is only in the sun for rigging and sailing then black is probably going to be OK. If you plan on leaving the boat in the sun all day every day then it would be safe to choose another colour.

If you choose to have a black boat they only have two kinds of finishes. perfect and crap. I kept this in the forefront of my mind when finishing my black boat and in the end you could use it as a mirror and many did. As black shows every minor imperfection it has to be perfect.
Regards,
Phill