After starting out as orange and turning green, Oscar took a detour of sorts in early 1974. (I base this on #573, which is not a Noggin show but one that was apparantly smuggled out by some PBS or CTW employee, and which by my estimate would have aired sometime in January '74.) The Oscar that appears in this episode is completely different from the one that had been settled on earlier and immediately afterward---he has much bushier eyebrows, scruffier fur, a beard, and---get this---moving eyes! They blink, too. Pretty freaky.
I guess this was an experiment that didn't work out. Either kids were scared of the new Oscar or the creators just decided it was too ugly (both are very possible
), but either way it didn't last long. It's odd that it seems to have been introduced in the middle of the 5th season, instead of at the beginning ( #536 and #560 still have the normal Oscar) But by the beginning of next season, the normal Oscar was back and, I think, replaced by a more familiar-looking puppet than the one before the "detour"
Here's Oscar, as far as I can tell (lotta holes, prob'ly)
the first--1969--orange, short fur
the second--bright green (sorta toxic-looking), longer, straight fur, bigger head
the third--c. 1974--scruffier fur, bushier eyebrows, moving eyes, beard
the fourth-- rest of the '70s--darker green ("spinach", I guess), more tangled fur, slighly calmer eyes
Since then he hasn't changed much, except it seems to me there was a period where, like Ernie, his head was smaller. I don't know when it was. I'm sure that, like the others, he's been remodeled/replaced umpteen times, but I can't spot or don't know about the differences (since he's almost exclusively a "street" character, his entire skit history wasn't always on display like Ernie's or Cookie's would be)