Cool!! I'd definitely be interested in the two Firefly ones if you're selling. I agree that it doesn't look like fading. The "Mon Petit Poney" on one is black, and the other is blue. I've never seen fading that would have that kind of affect.
I have the other two. The Diamant does refer to the twinkle-eyed ponies. I have this one, a puffy one in German and both French and German in a flat sticker as well. I paid somewhere in the $30-40 range for these. They're hard to find, but it's also a sticker image that wasn't ever released in the USA, so that tends to bring the price up.
As far as the Posey and Firefly stickers, the image is more common, even if the "Mon Petit Poney" is not. I would say $12-15 each for those. Definitely interested in the Firefly ones