… a plant containing similar chemicals was used for dying things blue, but these and others had low concentrations which make them difficult to work with and the color is more easily miscolored by other chemicals which often leads to a greenish tinge to the blue.
The “Indigofera tinctoria” consistently throughout history provided the most consistent color at the lowest cost.
(Photo: “Indigofera” is consistent in hue regardless of the mordant or type of fabric or yarn being dyed)