From The Empire That Was Russia: The Prokudin-Gorskii Photographic Record Recreated

Prokudin-Gorskii [1863-1944] intended his photographic images to be viewed in color because he developed an ingenious photographic technique in order for these images to be captured in black and white on glass plate negatives, using red, green and blue filters. He then presented these images in color in slide lectures using a light-projection system ... involving the same three filters."

The point here is that the photographer in question was taking pictures that, when put together, create color photos ... of pre-revolutionary Russia.