Mammals:
* Large: Elephants, wolves, foxes, kangaroos, gorillas, whales, dolphins
* Small: Rats, squirrels, mice, rabbits, bats, hedgehogs, opossums
* Domestic: Cats, dogs, horses, donkeys, goats
Birds:
* Common: Pigeons, doves, gulls, owls
* Birds of Prey: Hawks, eagles, falcons
* Waterfowl: Ducks, geese, swans
Other:
* Fish: Sharks, rays, some species of fish
* Reptiles: Lizards, snakes (some species)
* Insects: Moths, some species of butterflies
* Amphibians: Toads, frogs
It's important to remember that:
* Many animals have a range of colors, including grey.
* "Grey" can vary in shade and intensity.
* This is just a small sample of grey-colored animals. There are many more out there!
Do you have a particular type of animal in mind? I can give you a more specific list if you tell me what you are looking for.