Actually I think the Jack Muppet was rather skintone-coloured. I always saw him as more of a "Whatnot" (Muppet productions) than an "Anything" (Sesame). He looked a bit like one of the elves from "The Great Santa Switch", except that those had black mouths and Jack has a red mouth. He was a live-hand Muppet, too.
They used another "Whatnot" like that for Gone With The Wind (Guy's girlfriend).
The scene is from the 1969 Unpaved episode where (Orange) Oscar shows Susan all the preparations he made for Herbie the Grouch's birthday (Roses are red, violets are blue. Have a horrible birthday, we all hate you!"). In that same episode there's a song "I Am A Fine Musician" by four incredibly scary AMs. I dunno. They looked unfinished.