This is another one of the 2 by 2 foot tests I did on particle board.
The color is sort of nasty; purplish-greenish things do exist in nature, but usually next to a leaky chemical plant, or in some branches of the lettuce family (grown downwind of a chemical plant). Maybe in kelp, tired of waving at passing waves, washed up on shore?
I had to convert this from a Polaroid photo, taken from the side.