I've been getting pet achievements by adopting pets of different colors from Adopt R Us. I'm still missing the Hydrus, Storm and Angelic achievements. I was wondering if it's even possible to find these colors in Adopt R Us? (Hydrus is kinda special so it crossed my mind that a pet of that color might change into something more common when abandoned.)

Storm and angelic can be adopted (there was an angelic pet I found & adopted earlier for the achievement). :) Hydrus cannot. From Merana's page after completing her quest: "Note: The magic of this pet is bound specifically to its owner and this island. If this pet is put out for adoption, Merana's magic will no longer work and it will turn into its common color." ^^

Thank you!! :) Nice to know I can still keep searching for those two in the pound, at least.

You're welcome! I'm hoping for a storm pet to show up too for the achievement x) At least hydrus is cheap to make if you have the map :)