First splendida occur from a tiny bit south of here(Tucson) To the northern parts of the Yucatan Pen. They occur from sea level near the tamilipan (sorry for the spelling) to over 7000 feet in Nenuo Leon. I caught a black tharyi ten feet from a normal everyday Splendida. I have found them in Comstock texas(really big and weird ones), near blairs and alterna. I have found them thru out west texas and southern New Mex. And of course across half of southern ariz.
But, they do not occur in our hot deserts. In fact, they seem to perfer a little elevation(in Ariz) and concentrate around high grasslands and praires.
What I am getting at is, they are kingsnakes and surely have different head shapes, etc etc etc etc from area to area. With the black types somehow right in the middle of them. Kinda reminds me of striped kings.
Now FYI, many desert diurnal snakes are black, as many highly nocturnal snakes are lite colored. Wow, isn't that odd?
Heres the deal, black absorbs or better yet, does not reflect color. So yes, a black snake can heat up very quickly in the sun. But, this is the part 95% of people forget, black skin does not contain a one way valve. It also allows heat to escape quickly. Bingo, it allows black animals to cool more efficiently in the shade.
Since you anthro'ed your post, let me ask why are equatorial peoples dark skinned, wide nosed and curly haired?? They occur in the hotter or hottest climates in the world. I think you already know, they are designed to emitt heat and cool faster.
A little story, I was in northern central australia, at a tiny roadhouse in the middle of nowhere. I looked across the road and saw a bunch of aboriginals sitting out in a field. There was no trees or bushes, they were just sitting there. I asked the barkeep, what are they doing there? He said, "They live there mate" I looked at him and said, HUH? yea mate, thats where they live alright. I asked, why don't they go over to those trees by the billibong, he said, they have no need to mate. IT was about 110F out.
So consider, black has one ability to do two things, its transfers heat, in and out. Thanks FR