It'd be more convenient if you didn't need the colon in order to use the "comment" tag (for example) without a description. Software like iTunes can only read the description-less comment tag from ID3; so it should be convenient/obvious to write.
The following should ideally work
At the moment to achieve the desired behaviour I think you'd need to have a colon after each of them.
I think the same possibly applies to the performer and lyrics tags too.