Trichrome
Trichromy ( borrowed from ancient Greek τρι tri = three and χρῶμα chroma = color) is a method of color photography in which three separate black and white photos are made using the color filters red, green and blue, which are then overlaid again for viewing in color.
The merging of the three individual shots to form a color image is done in the classic way on black and white film by positive development of the images and subsequent overlaying projection through appropriate color filters. The color separations can also be put together electronically in EBV software.
The difference between trichromy and the color photos commonly used today, in which the filtered black-and-white images are always created at the same time, is the staggered recording of the color separations.
The process has been known since the late 19th century and became possible when black and white recording material with panchromatic sensitization was available.