thoughts please...

[Bogertophis]

CA is Central American locality of Bi (boa imperator). Majority, at least in the past, imported and bred Bis in captivity were from the Colombian locality with Bc (boa constictors/true red tails) coming from further in South America (Surinam, Guyana, Peru Brazil). Lots more CAs in captivity now and some are further referenced to point of origin such as Nicaraguan. Main differences (generally speaking) are that CAs tend to be smaller. In general they usually have darker, heavier patterns but with normal boa variability that isn't as set in stone as it used to be. CAs were generally thought of as being hissier babies as well but again now with more numbers in over the years, it's not such a hard and fast stereotype.
hope that helps?

That's apparently what my late BCI was (she was also referred to as a Mexican BCI but she was being offered free with little info). Anyway, she fit your description
to a T: dark in color & very defensive (hissy & a skilled biter, lol...that resulted in her being "free"). She actually became a sweet cuddly boa with a little patience, and
her dark coloration made for some stunning iridescence in the sunlight.