It should be on on every OS version, even on Desktop OS. It's a security meassure
Indeed, KMS should be a no brainer. Just setup (let it be a role or other, don't care) and add the license keys. Same procedure for OS as for Office licenses.
Great suggestion. I'm searching over many years now for something like that. It should be easy to implement, after all it is already done for encrypted (green) and compressed (blue) files.
Just 16 colors would be more than enough.