I've once read a fic about a FanClan called BlizzardClan that lived in the snowy mountains (not the aussie mountains, but just snowy mountains) and since they need the camoflauge, they abandon any kits that have pelts that are not white, gray, or silver. What do you think about it?
Here’s something interesting about camouflage: solid colours are very rarely a good idea. Solid-coloured animals, of any colour, are often at a disadvantage in comparison to their multicoloured or patterned counterparts.
There are few environments where solid colour is more effective than patterned, because one of the key purposes of camouflage (in many cases, but not all) is to break up the shape of something: the idea is to not have a distinct silhouette but instead to blend in with the uneven colours and shadows of the environment.
It’s called crypsis, if you want to know more about that.
Very few environments are only one colour, because shadow, foliage, rocks, and other factors are still a part of it. A snowy mountain might be largely white and grey, but there’s still going to be rocks, there’s going to be vegetation, there are still going to be shadows and light, because if there wasn’t, there would be no prey or predators. It’s an ecosystem, even if it is a harsh one.
Additionally, many animals have very bad colour sight compared to humans. In real life, cats have a very limited sense of colour, so grey, orange, and brown are all basically in the same spectrum to them. So is green. But even if your clans can see detailed colour (you can take artistic liberties, after all), there’s no need to assume that other animals have broad vision too. Brown, orange, and grey could very well still look the same to a rabbit.
Basically, what I’m saying is this idea doesn’t hold up well under scrutiny. There’s no actual reason for kittens to be abandoned by this clan, because the premise of “cats that aren’t white, grey, or silver won’t survive/won’t be able to hunt” is actually false. But that doesn’t mean it’s not a fun idea to play around with! Things don’t need to be 100% factual truth to be fun to write and read about, especially in speculative fiction genres. You’re allowed to have fun with your writing, even if you have to suspend some disbelief to do so.