In two episodes of The Muppet Show, there's a group of full-body clowns, but both of their scenes feature black backgrounds. What's the deal with only putting those clowns in front of black backgrounds? They're costumed characters, they don't require the performers to dress in black and hide themselves. Though their second appearance did involve performers to dress in black, but for a different character.
And both appearances by the clowns were for sad-sounding numbers that had to do with clowns or the circus. Maybe the sad nature of the songs was the reason for the black background, but I'm sure those clowns could have been used for some livlier numbers (I think the Shields and Yarnell episode features a rendition of "Make 'em Laugh", that sounds like a good opportunity to use clowns).
And when it comes to full-body characters on The Muppet Show, it seems like each of the monsters (okay, not the one from Doug Henning's act) were in quite a few episodes, but all other full-body characters appear in relatively few episodes (okay, maybe all the monsters weren't that major, but compared to these characters they were used a lot). Fletcher Bird, Betsy Bird, the bird dancers, the spider, the lion, the giant pig....