I am searching patents. Many interesting finds.

First is 2930691 , applied at 1955 and issued at 1960.

This invention relates to color pictures formed by dye absorption and more particularly to matrices used in printing pictures by imbibition , that is by transfer of dye from one or more dye soaked matrices to a dye absorptive layer of gelation or the like using three matrices representing the three colors of scene and containing cyan , yellow , magenta.

.... imbibition pictures have relief matrices have... shadows and highlights represented by hills and valleys

This patent covers FLAT matrices not RELIEF

Patent writes as well known acid dyes used at relief matrices , these flat matrices uses the same

There are many examples per chemistry
Bleach and Tone

I will continiue to short the patents.