i noticed I had an option on my pet of plucking a feather and my pet will lose its deviance.

What is a vermillion feather and what will it do?

The Vermillion Feather is one of the materials needed for the Carpo Kami Event. You need one vermillion feather to craft a Phoenix Autumn Wreath. It's currently an item that is very much in demand; you must acquire one if you want to get Carpo. And it only comes from deviant rocs.  If you pluck that feather, you could sell it for a great deal of money or trade for rare pets/items. 

Ooh! Wait, I'll check the trades...

But then your roc becomes non-deviant! So you have to decide if you want to keep your roc deviant or not.

I won't pluck it, but it isn't much of a deviant anyway. The only thing making it different is two orange feathers sticking out on it's head, it's really funny. ^-^

don't bother checking, it only shows adult form when I search my pets.

It's an adult now. I also have a deviant unicorn that will look like this when it grows up:

Picture wouldn't show :/

It looked like a glowing cremello! ^-^