I can't find the anthropology paper, someone with better googlefu can help maybe.
There is evidence going back and even today that many ground grains seeds and plants were used as bases for Dyes rather than as food. Considering the difficulty to gather, process etc.
Millet and Sorghum are prime examples
This argument makes ancient ground grains suspect in my book and makes sense
Can you share any papers reports or studies for or against this idea?
Edit:
Amaranth is so prominent an ancient dye, its a color.

