01
Read what the image actually shows
Black-and-white photographs distinguish tonal values rather than product colors. Later colorization, print fading, and reproduction can introduce further uncertainty. Use such images to study course patterns, shapes, and architectural relationships, but avoid identifying a quarry or exact color solely from a gray tone.
02
Seek complementary evidence
Look for documented specifications, surviving material, or other reliable records and have them assessed together. If the color remains uncertain, record that limitation in the design decision. A transparent selection based on the available evidence is more defensible than claiming an exact historic match that the photograph cannot demonstrate.