From Twitter: 
“Fun Fact: according to Sesame Street canon, Oscar is and always has been orange, he's just coated in green filth. I recall reading that the ONE time he washed himself he briefly became orange again, but hated it so much he covered himself in grim and became green again.”
I recall Spinney making a joke about the first part (I can't remember where), but I've never heard the bit about it actually happening on screen.
Anyone know if there's any truth to this claim? Sounds like it could be a retelling of someone's false memory, but given the weird stuff we've uncovered lately, it's not entirely impossible either.