So what did the famous Irish-American and his equally celebrated amphibian-American friend sing? Well, "Bein' Green," of course, Kermit's signature ballad about the difficulties of accepting what makes us all unique.
"It's not that easy being green," began a forlorn-looking Kermit, "having to spend each day the color of the leaves. When I think it could be nicer, bein' red or yellow or gold or something much more colorful like that."
But soon enough, Fallon arrived with some reassuring words. "Today's the easiest day to be green," he reminded Kermit. Then they sang in unison: "We are green, and it'll do fine. It's beautiful, and we think it's what we want to be."
This isn't the first time Fallon has collaborated with the Muppets. Last month they teamed to bid farewell to "Late Night" with an adorable rendition of the Band's classic tune "The Weight."