Is there any thread or database somewhere that shows what some of these do? I'd like to see what colors I'm changing my pet to before I do so. (E.G. is dusk shades of gray or is it blues and purples?)

Here ya go

Subetalodge has a list of all of the pets by species and by color. Here's the color one: http://www.subetalodge.org/pets/sort/color

You can click on a color to see what all of the species look like in every color. A colored potion (like an Arid Potion, for example) will turn your pet that color but keep it the same species. And elixir will turn your pet into the color/species combo of the elixir (for example, if you have a Mahar but want to turn it into a Bovyne you could use one of the Bovyne elixirs for whatever color you want).