The Polaroid 35mm instant color film was akin to Autochrome -- filter stripes above the emulsion (so both exposed and viewed/projected through the same stripes), and an "instant" processor (took thirty minutes, as I recall) that produced a direct positive. Single layer -- black and white panchromatic film under the filter stripe layer -- and the filter stripes were so narrow they were hard to see in the film even with magnification; the stuff actually projected more or less okay.
I've forgotten (if I ever knew) how they got a direct positive from what amounted to a monobath process; it wasn't a pre-exposed film like a couple direct positive materials I've read about. Perhaps it was dye destruction like Cibachrome (which would be both simpler and faster in terms of film speed with just a single layer). Or maybe the processor actually developed, bleached, and redeveloped, a true B&W reversal process.