Does using a pet species potion also affect the color too? Or can you change the species and keep the color along with it?

If you use, for a example, a Jollin potion, it will become a common Jollin. If it is a Field Illumis Potion it will become a Field Illumis.

So yes, the colors change too, you can't change the species without changing it's color, at least from what I know

Ah all right. Thanks.