I'd guess that his gnarly, creepy style was probably half the reason people thought D&D was satanic.
His cover-art tended to have surreal, glaring colors. But most of the drawings are black and white, begging for coloring. Except who would dare to sully a vintage game supplement? (seriously, half of the old D&D books I've gotten from used book stores have atleast some of the illustrations colored in)
So here are some uncolored scans , straight from the internet.
I present the Erol Otus Coloring book!
Does anybody know what monster this is? It looks like a pumped-up carrion crawler.