As you pointed out, the difference is that the colon : is an illegal character
and the semi-colon ; is perfectly valid, while retaining visual conformity.
If a tag title contains the colon, it has to be replaced by a valid character for the file-name.
Alright, we all know that.
The proposed characters are (as far as I know) valid on all platforms and logical substitutes,
so I don't know where you want to "be on the safe side".
Still, if this request was going to be implemented,
a simple option to "replace illegal characters with space" should be the lesser problem.
At least it would be self-explanatory to users, and they'd know what to expect from auto-organisation.
Consistency is important to me, not the illusion of organisation created by mere tag management.