Jasyn, what you probably have is a black or chocolate kuhli. There are 15 species of genus Pangio listed in the Loaches.com species index. They're all recognizably kuhli loaches, and there are three that are only commonly known as kuhli loaches, Pangio kuhli, P. cuneovirgata, and P. malayana. My kuhlis are, in fact, P. myersi, Giant kuhlis. Yours is probably P. oblongata, though if it's a textured rather than solid brown it may be P. piperata. They all have pretty much the same requirements, though.
Lot's of kuhlis do change patterns as they get older, but this isn't one of them. They stay brown.