Peas that have been stored for a while tend to lose their bright green colour and turn dull or yellowish, which makes them harder to sell. To disguise this, some traders dye the peas using malachite green, a toxic industrial colourant, to restore a fresh looking green shade. A simple check involves rubbing a wet cotton swab on the peas, and if green colour transfers onto the cotton, it confirms the presence of this dye.