This is Black Phase Boaedon Fuliginosus... most of them are light to chocolate Brown Hence Common Name Brown House Snake... but From Nigeria to Liberia this specie present with another color with is Dark dark Dark brown to black... Parents was WC import from Benin. Is Hard to say is a locality or particular melanistic mutation...
I will go with Locality especially that from 10 Babies I got I didnt gey Any Browns.. all of them are Black some of them even Darker than Parrents