This has my vote.
Some thoughts:
Burst - increased illumination radius
One of them, charged maybe providing glare instead of spotting, making the cloud less transparent
Loch - if rainbow is a bit much maybe having it give a shorter, much more intense burst of light, bigger than burst even
Novel effects for novel guns - currently the way it works is that ammo has the same effect on every gun (excluding effects that themselves have no effect), i think as would be needed for this there should be an exception for unusual guns, the harpoon certainly and maybe the minotaur, flamer or mines (although mines allready get an interesting variety of effect)