Answer: archil

AnswerCrossword Clue
archila violet dye obtained from lichens (genera Roccella and Lecanora)
archillichen that yields archil
archilany lichen yielding this dye
archila red or violet dye, also ORCHEL, ORCHELLA, ORCHILLA, ORSEILLE
archilviolet coloring matter obtained from certain lichens, chiefly species of Roccella