AFAIK, this is the first BLUE BFG that ever was... I know, because I did it!
Started as black, got stripped, very lightly sanded, dyed, and lacquered. The top lacquer is a few extra coats to help smooth things out a little. Rewired "my way" to give the extra "middle" tone control, and extra selector (chicken head) that does standard 3way parallel, out of phase, and series.
It didn't stay blue for long... and has settled into a sort of teal color from the dichroic dye separation and the lacquer yellowing.