Here's a look at the still slightly wet matrix on photoformulary subbed melenex[sic]. Once dry it became significantly thinner (if you can even tell).
Tartrazine has been the standard "extinction dye" for color-blind matrix materials since the beginning, with Ives in 1914. We all likely consume some of this coal tar distillate every day in the form of yellow 5 of FD&C 5.
This coating is 5% per volume of classic McCormicks food coloring.