Last iteration (which was a long time ago) it was played as the more fantastical interpretation of light, so holy and divine, with healing magic and such. If using a literal approach, it'd be really hard to think of more than one use for darkness magic, eh? That said, if you prefer to stick with true light manipulation and leave healing out of it, I'm sure that's allowed.

Edit: Guess you went for fire after all (I think?). What's with the 10-year-old characters? :P