Maybe you are right. Manufacturing techniques and all have advanced since the Henson era. Who knows, if Jim was around today maybe they would be more perfect. It was just purely conjecture as Disney like everything "perfect".
That's what I'd say too. I highly doubt Disney made any of the big decisions about what the characters should look like. If they did have anything to do with brighter colors, I didn't quite notice it.
Is there any truth that Fozzie's fur isn't even manufactured anymore? Some of these things can't be helped... though I still don't get Muppet Babies nose Gonzo. That's the only glowing example.
But this isn't something Muppet/Disney exclusive...
Take a look at Sesame Street's Prairie Dawn
This is her older look, a smaller head, much more expressive, eyes very close to the mouth... very whispy looking.
Now check out her more current look...
on the one hand, the character's more consistent looking from appearance to appearance, but the head construction is much stiffer, and therefore less expressive. She even looks just a little bit bigger. it's like looking at 2 different characters almost.
Puppetry technique changes and grows, and sometimes it becomes so over perfected, the little flaws in the material get ironed out, making them much stiffer overall. Let's look at 2 different Ernies...
70's-80's Ernie
modern... you can see his head is now perfectly oval shaped, almost rounder... his hair is too perfectly neat, and over all, doesn't quite look as expressive.