It has been called industrial melanism because the mutation that made the insect black was concomitant with the industrial revolution in England. A soot-coloured butterfly has a better chance of surviving on a soot-polluted birch.
gene pannier is active in different populations of elytra cells that prefigure exactly where the black pigmentation will appear in adults. Pannier then activates other genes that collectively ensure the production of black pigment by these cells and thus the formation of the black spots (in “red” ladybugs) or the black background (in “black” ladybugs).