Toon Standard's "Rim Lighting" feature is a nice way to add some nice subtle variation to a material -- the only problem is, it has the exact same brightness on screen regardless of any other lighting conditions, which means that an intensity value that's nice and subtle in direct lighting, looks like a permanent surreal neon glow as soon as that same avatar steps into a dark environment.

I'm not certain what's happening inside the shader, but my guess is: the "rim lighting" effect seems to be added over everything else with just an alpha blend that totally ignores the lighting that was already on the character? Maybe adding an option to instead use an additive blend would let a subtle rim light be equally subtle in both light and dark conditions? (There's possibly also solutions involving multiplying it by the intensity/color of environmental light sources, but if I'm picturing it right, even just the additive blend rather than alpha blend could be enough to address this.)