for most colors, you'll use a potion. for instance, if you want a spectrum pet, you would use
a few colors (hydrus, galactic, nostalgic, steamwork) are different and require a quest or similar process.
ALL BASIC COLORS: arid, cherry, common, cream, dawn, dusk, field, gold, lilac, marsh, nuclear, silver, sun, twilight
ALL SPECIAL COLORS: angelic, blacklight, bloodred, chibi, darkmatter, galactic*, glacier*, glade*, graveyard, hydrus*, nightmare, nostalgic*, reborn, scribble, spectrum, steamwork*, storm, and sweetheart.
How to get a galactic pet
To obtain a Galactic pet, you must finish a quest for Itallo, who resides in the Coda Caves of Atebus. He will ask you to bring him a certain amount of coda caves crystals, which you can dig for free in the Coda Caves. However, the caves are only open for a very short amount of time every month [6th and 7th day of each month]. Remember that receiving Itallo's blessing on one of your pets will only change its color, so if you want a certain species, you must first use an elixir on it, if it's not already your preferred species.
how to get a glacier pet
You can either purchase a glacier potion, or you can create one yourself - which is usually cheaper, although might require some luck.
= +
You will need an artifial prism chalice, which restocks in the Millionaire Center, Centropolis, and you will need to find a bucket of polar water by searching the polar ice fields in Arctic Frost. (this is the part that will likely take some time.
When you have obtained both Artificial Prism Chalice and Bucket of Polar Water and have them in your inventory, take them to Asmodeus's Genetech Lab in Darkside and combine them to create your glacier potion.
how to get a glade pet
To obtain a glade pet, you can simply purchase a glade potion, or you can create one yourself. To do that, you will need an ornate floral pitcher (token shop), which you then go fill in the Peka Glade. The Glade is open every day at 8am and 8pm, but only at those times.
= + peka glade water.
how to get a hydrus pet
To obtain a hydrus pet, you will first need access to the Omen Islands. To do that, you must collect all nine pieces of "Uncharted Map" - either by buying them from user shops, or waiting for random events.
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Then you will be able to visit Omen Islands and its resident sea goddess Merana, who will ask you to bring her a selection of items in exchange of cursing one of your pets hydrus color. There is no available hydrus potion.
how to get a nostalgic pet
Here is a handy tutorial how Vanya's Workshop works!
Basically there are two parts to obtaining a Nostalgic pet. Either you build your toy from Vanya's instructions and the quest items he asks you to bring him, or you can skip the first part of the quest and purchase a ready-made toy, and only bring that and an Essence of Melody to him. Essence of Melody has usually been a gifted to users every year if they visit Melody's calendar every day during December (1st to 31st), but it can also be purchased from Cash Shop.
how to get a steamwork pet
To obtain a steamwork pet, you will need a schematic and a yunium key, which you then take to Yun Enterprises.
Yunium keys can also be created in the Genetech lab, by combining Steamwork Key Stone Mold + Yunium Ore + Melting Kettle.