Hello! I remember sometime during sarah's tutorial that she showed me a room that showed all of the colors for each pet I had unlocked. She also said something to the effect of "you don't have to use a potion (or whatever colors them) again if you have already been that color. You have unlocked the color and your pet can be changed back to it. Now I cant find that however :(
Anyone know where?
There's no such thing as unlockable colors. Your pet has one color, the one it currently is, and that's it.
If you want to change the color of your pet, you have to either use a potion or an elixir.
[Item=reborn potion] = turns your Common Lain into a Reborn Lain
[Item=Field Pherret Elixir] = turns your Common Lain into a Field Pherret
I think Sarah might just have shown you all possible colors or a few examples, I don't remember the tutorial though.