This could be an early dye transfer print using the "two-color" process.
Kodak made the relief matrix material and dyes for Technicolor two-color motion picture film at that time, but the Kodak Dye Transfer system that used three-colors for still photography wasn't introduced to the public until the 1940's.
Being that it LOOKS like a two-color image, I would speculate that there is a good chance this Johnstone might have been experimenting with dye transfer prints as part of the eventual release of the three color system, but that is just pure speculation.
Please contact The George Eastman House Museum at
https://www.eastman.org/photography.
If they don't know about it, no one does...