But here's a quote from the instruction sheet for color print retouching colors offered by the SPOTONE/Retouch Methods Co, Inc:
"Though these colors have been designed for use with the Ektacolor and Eastman color print papers they can be used with the same confidence on other color prints made with the color papers of other manufacturers."
"...They will penetrate into the emulsion, becoming a part of it and leave no surface residue. The retouching and corrections will be invisible."
I assumed they were similar to Marshalls. And Kodak Retouching Dyes for that matter. I've used them to colorize B&W prints, unsuccessfully. I'm not good at it, I don't have the patience.
There's a masterfully done still life B&W photo colorized by an artist named Clint Eley, using retouching dyes, found in the book: Handtinting Photographs; by Judy Martin & Annie Colbeck. He spent two weeks on it.
I've done much work with the oils and pencils on restored photos, people pay double for it. Not for the ones done with photoshop - no FB paper.