If you setup Missing Buffs on a character and then logs onto another one that does not have the buffs you setup, the square will be there, but blackened out.
It should preferably not show at all.

https://gyazo.com/be8517249de5f952ecbaca24f3467f2d

Edit: I guess using profiles could solve this. But for someone using the same profile for every char it should probably just not show the square if you don't have the spell.