Up here in Denmark solid black - except for the yellow nuchal blotches - is the norm for grass snakes though some are dark slate gray with a faint pattern. My local adder population also has a majority of black individuals and melanistic vivipara are supposedly not all that rare. I've never seen one, though. The specimen shown here is - as others have commented - stunning.
So, who will post a gotlandica, carbonarius, black asp, ...?