Metal Foil Color Print Processes 1930's-41?

Yesterday I was shown a color print made by a machinist for the Palomar observatory who was also an avid photographer.

The base looks like matte aluminium foil on single weight paper. The "colors" appear to be dyed gelatin, although I can't tell if there is one or many layers. The back reads "San Jacinto Mountains, negatives 1931" I find it interesting that it says "negatives" plural - in camera separations? The image is 6x9cm, the print a few millimeters larger. Any guesses on how it was done?

Must be one of the 'assembly' methods. Assembly because the primary colour images each lie in one thin layer; the aluminium foil was probably used as the base to provide maximum reflectivity and allow the coloured layers to be seen through. One guess is that each separation negative was printed on a positive material where the positive image is either replaced with a dye or else toned, to produce the CMY primaries. E.g, the red negative is printed to form a cyan positive, the green, a magenta positive, and the blue, a yellow positive.

I think I've seen something similar in the colour section of very old recipe books- the thin gels are all bound on a page, and when separated, they are actually individual positives coloured in one of the dye primaries.