Dry ginger naturally has a dull, pale yellowish brown colour, but many buyers associate a brighter, whiter look with better quality, tempting some traders to bleach or brighten it artificially. Ultramarine blue is a synthetic pigment used for exactly this purpose, giving dried ginger an artificially whitened appearance it would not naturally have. Since this pigment is not an approved additive for this use, its presence in ginger counts as adulteration.