Color Photography Explained-2
The first step in reproducing a print on paper is to separate the color positive made in the camera into its three respective elements, namely its orange-red element, its green element and its blue-violet element. This is done by photographing the color positive successively through glasses covered with colored gelatins corresponding to the three primary colors. For reasons which will be explained later, the printing is made not in the primary color but in its complementary color. This picture shows the negative made by the orange-red separation filter, printed in its complementary blue-green.
This image is from: Luther Burbank: his methods and discoveries and their practical application. Volume 12 Chapter 6