These all sound really cool, although my favorite suggestions would have to be the supernova/aurora and beach ones. Outside of basic poses and the occasional Nostalgic pet(plus scribble and chibi), we don't have a whole lot of bright color schemes for pets, and the aurora color could bring in some saturation. Plus I really like blue/green color schemes. :D

Hydrus is nice for the ocean element, but sometimes the brown color scheme just doesn't work. Maybe if a coastal/beach color doesn't work for some people(which I get; the main beaches I've been to were gray or black sand, with maybe some seaglass or shells), it could be more of a coral reef type thing? With sponges and other reef elements and bright colors?

I'm not totally sold on battling as a method to change colors, though; for example, unlucky Ice King losses can happen, especially if you're right at that level where you can sometimes beat him, sometimes not. I have a Reborn battle pet, and I would've been pretty annoyed if I had to fix his color every time I lost, especially if I hadn't already unlocked Forj. People shouldn't have to avoid Ice King or pay CSC just to keep their pet color. Everything else that changes color is pretty deliberate, and usually accidental pet color changes just occur from human error(zapper, galaxy quests, etc.).

Edit: Maybe instead of using the Ice King, magma could be earned by getting to the end of the Ice Fields? Like, you would reach the end and there'd be an option to investigate further instead of just taking the bucket, and you'd find a pool of ice water or something. There'd be a message remarking on how cold it must be and how it might have a cooling effect on certain pets, and you could dunk one of your Reborn pets into the water to change it to Magma. If you don't have a Reborn pet or don't want to change them, you could still pick to just take the bucket and leave.

Oh my gosh, I just found this thread, and I think "second-level" pet colors would be a totally fantastic thing to have on the site c:

I'm especially intrigued by the Supernova/Aurora, and Riftborn OwO

flails all of these are so cooool! I love the spirit and skeletal ideas!

Yes, yes, yes, especially autumn. It's a little too easy to change colors with a potion.

Even some of the 'boring' colors that are just recolors could benefit from subtypes, esp. subtypes that upgraded them to colors with new poses. For example, I don't like galactic pets because they're very busy, but I would love pets that were just deep blues with flowy, nebulous lines and constellation-type markings. Call it stellar or starlight, and have it be what happens when you dose a twilight pet with a dusk potion. It would help increase prices of basic potions if they were a step to flashier colors.

these would be cool ideas! like a quest to get one color and go a step further for another cooler color! :D