Well I painted my old 200x Mer-Man. I didn't like the plastic color and the fact that his trident/sword/scale looking armor that appears to be made of tooth/bone was all this glossy brown. So I painted the plating on his chest and the tooth like parts of his trident bone white, then I dirtied it up a bit with a light brownish yellow. I think he looks good.
Try some bone white. Add some yellow to make it look decayed. If you hate it, wipe it it off and do something else.