Rex just has a darker complexion and dark hair… he’s just meant to resemble Jason Mantzoukas more. In the comic he was just more fair in appearance.
Amber just isn’t that important of a character, nobody is attached to a particular image of her so most people don’t really care if it’s changed. If they made Atom Eve look different would probably be a different matter.
Personally I’m picky on details so the fact that Monster Girl has dark brown instead of light brown hair and that half the characters have imo ugly bangs bothers me way more than anyone’s skin tone changing.
You could read that as him correcting himself from accidentally telling the truth that it’s a few weeks away and that he is not able to disclose that yet.
I suspect they at least don’t have a firm date yet, but I still think it’s most likely because they aren’t done yet and it’s going to be more like months.