Making prints using color separation negatives requires the preparation of three large negatives from the same original image, often a color slide. One exposure is made with red filtration, one using green, and a third negative is made using blue filtration. The three negatives are each printed on to the same piece of paper using consecutive coatings of gum and watercolor pigments of the complementary color to the one used when making the negative. The red filtered negative is printed on paper coated with a blue (cyan) pigment, the green one on magenta (crimson) coated paper, and the blue filtered one is printed on yellow.
Choice of pigments is a matter of artistic taste. Sources frequently recommend Cadmium Yellow, Alizarin Crimson and Pthalo (Windsor) Blue. A more pastel pallet consists of Cadmium Lemon or Light Yellow, Alizarin Carmine and Cobalt or Intense Blue. The order in which the paper is coated and exposed can also vary. While the usual recommendation is blue, then red, and finally yellow, I find that the reverse often works well, particularly with subjects that are basically warm toned.
While perfect color filtration is unlikely and further negative masking frequently required to produce complete color separation, the resultant print reproduces the colors of the original. The steps involved in the process and the color theory involved is outlined in "The Gum Bichromate Book, Second Edition" (Focal Press, 1991 by David Scopick.