Ok, thank you.

Normally, strings, ending with a colon (:), are used in forums as labels of an input field. Does this information help ?

Well, yes and no ...

The internet site of "L'Office québécois de la langue française" do not use (:) in forms (at least in one form to communicate with them) !

I guess it depends where the label appears: left, or above, or under the field.
All styles seems to be Ok.

I will use the (:) the same way than MLF.