The art only exists for some creatu, so not all of them are able to be blessed yet. Currently from Atquati, you can bless Ahea, Draqua, Goiba, Quelis and Skaldyr.
Also, you can still bless calico creatu even though the preview doesn't work properly. It will show a natural colored creatu instead of calico. But no worries, it doesn't change the color of your pet.
Finally, the creatu only shows its effect if it's an adult. You can bless younger creatu, but you won't be able to see it until they're aged.