Okay, I literally never post, but I had to see if anyone else has a pet like this. So I'm playin' some Adventure, right? Used Egg Potion to get Vivid Draook. It hatched today, and it has a star on its picture! It still looks mad, like it did when I battled it in Adventure. Its designated as a Rare Vivid Draook. The "Rare" in its name has a mouse-over tooltip saying:

"Vivids have a 5% chance to hatch as rare"

Anyone else found one?

yeah! a rare vivid pixpet keeps the angry look that it has when you're battling it. it doesn't do anything else, just has a slightly different sprite, and admittedly on some pets it's less prominent than on others. I've only got a rare vivid nightshade so far but my current goal is to get a rare vivid nurbun :D

Oh, that's pretty cool!

Yup, I found one, and wasn't sure what was different at first:

It's probably subtle on some pets, like Veemooth here
*cow snort*