Can Aniimo have alternate colors?

That makes an odd-looking Aniimo something you run into rather than something you work toward. The variants are part of normal open-world spawning, so the way to see one is to keep encountering Aniimo in the field rather than grinding a single spot and hoping.

The roll can also come with more than looks. An Aniimo with perfect potential and distinctive coloration can turn up by chance out in the world, meaning the strange-colored one standing in front of you may also be the best version of that species you will meet for a long time. Stop for it. You are not just collecting a skin.

Umbral Aniimo, also called Umbra Aniimo, are their own thing and also spawn naturally and at random in the open world. Do not assume every unusual Aniimo you spot is a color variant, and do not assume a color variant is Umbral.

Catching one when it shows up

The Tumbler gives increased capture success in specific situations, climbing to a 6x multiplier during gather events. The bonus is situational, which is the catch: a wild variant can wander past at a moment when nothing is boosting your odds. If you find one outside those situations, you are working with your ordinary capture chance, so bring whatever you would normally bring for a catch you cannot afford to lose.

Not settled: How often alternate colors appear, and whether distinctive coloration reliably travels with perfect potential or the two just sometimes land on the same encounter, is not settled.