Black inks were often colored with carbon, and shouldn't fade.
Red generally will fade with light exposure, but at the time there were competing red pigments. Some of them were more colorfast than others.
The exact color was also mixed by hand starting with a base color and adding small amounts of others to adjust it to exactly what was wanted. And if the pressman was slightly short of base or ran low adding a little of something could extend the existing ink just enough to finish the days work (Or shift)
But of course, if you put in too much white, or extend with a tiny bit of white your red will be lighter.
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