Stephen Colbert swung by Late Night with Jimmy Fallon to perform Rebecca Black’s”Friday,” following through on a bargain he struck with Fallon earlier in the week. (Fallon had held up his end by successfully raising $26,000 for Donors Choose. Which, when you think about it, means that Rebecca Black has evolved in the span of a fortnight from “adorable national punchline” to “legitimate force for good in the world.” Hey, what did you do with your last fortnight?) The performance is, in a word, fun. In four words: Fun fun fun fun! Colbert croons the opening lines, alone on a darkened stage in a Dean Martin-worthy tuxedo. Then the Roots strike up and make “Friday” sound like a funky-kinetic anthem for a generation that hasn’t been invented yet. And look, fireworks! A surprise appearance by a former American Idol! Who plays the harmonica! Jimmy Fallon sings a verse with ironic auto-tune! And that’s about when the Knicks City Dancers appear. Check out the video after the jump…

What do you think, PopWatchers? Better than the original? Think it would’ve been more fun with David Cook? Will “Friday” someday compete with the Beatles’ “Yesterday” for most-covered song ever?