nope, not at all... They were more 'stumbled across' than developed... Here's the article explaining...
http://www.elacuarista.com/secciones/tfhblue.htm
We cannot "create" a genetic mutation such as albinism, leucism or whatever ism the Blues are. We can only find them.
We can find fish with desirable traits and breed them with other fish with similar desirable traits to further 'bring out' such desirable traits. This is what is meant by 'line breeding'.
Or we can find fish with an 'ism' (or genetic mutation) that makes them special and follow the proven path of producing offspring with the same ism.
In my experience, a confident, strong, healthy Dempsey will get and stay dark and some will even get jet black. But take the same fish and put it in a dirty tank with stronger aggressive tankmates and you'll turn it into a much much paler fish.
I think all this talk of "Black Dempseys" as a "new morph" or "genetic mutation" is potentially misleading speculation... Enjoy your happy, healthy, confident & beautiful fish, but no need to fabricate some justification for it.