 At the beginning of the film theres a disclaimer explaining that  the strange look of the film was intended by director  David O. Russell (qv). The vibrant color is due to the fact that  they used "Ektachrome" slide transparency film instead of standard  film stock, and the "bleach bypass" process actually gave the prints  a much deeper black. The silver halide is completely opaque, thus a  "true" black. Leaving all of that silver on the prints resulted in a  much higher cost for distribution however.