It would help if you could explain where you see this on pets? The only example I know of where there are BLUE and YELLOW exclamation marks on pets is if you have the Pet Tracker addon installed.http://www.curse.com/addons/wow/pettrac ... creenshots
(Screenshot 8/10) the Spring Rabbit has a blue "!"
This means that this pet is only available as part of a world event (Noblegarden).
A yellow ! means that this pet is attainable when you complete a normal quest