There isn't a potion for this pet color. Here's an explanation of how these pets work, copied and pasted from this post
The prices of the toys and instructions and all of that can be pretty varied, so it depends on which pet you want.
It really depends on what kind of pet you want. The Plastic Molders Kit and Wood Carvers Kit can both be found in user shops for less than 100,000 each. But the Plushie Makers Kit is in shops for over 3 million right now. Plus whatever other random items he asks for.
there is no time limit on how long you need to get the sP to buy whatever Vanya asks for, and his "items asked for" is quite varied so nobody knows the true answer to your question. If he happens to ask for expensive items and you are using an expensive Instructions then you will probably want to save for a bit. You do not need to worry about the time taken to do this. I think you can quit and try again though so if your Instructions were cheap enough to buy another copy, this might be a way to go.
sometimes it's actually cheaper/easier to simply buy the toy from another user and bring it to vanya along with the essence of melody. so for instance if i wanted a nostalgic devonti, i would bring vanya the following two items:
doing so will then make your active pet a nostalgic devonti, for instance.