[Sombre]

This is just how I'd initially approach Tzeentch magic, so it's a bit rough.

Red Fire - An accurate (prec 10) midrange fire ball type spell that does aoe 1 18 damage, but can be resisted by mr.

Yellow Fire - Either a small aoe fire shield buff, or some sort of protection buff. It gives a 5+ ward save in warhammer to mage and his unit, which basically translates into a defensive buff of your choice.

Green Fire - Just a Tzeentch version of confusion, really.

Blue Fire - An upgraded version of red fire. Prec 20, better range, more damage, more AOE. Again, can be resisted by mr.

Indigo fire - In warhammer this spell kills enemies and produces horrors from their ashes. It's nasty as all hell. I guess there are a few options here, but what I'd go for is actually a combat summon of a handful of a special kind of horror which has flying (representing them being cast forward by the caster) and does weak but aoe red fire esque damage as its melee attack, coupled with a nice explosion sprite which will cause them to look 'staggered', going off one by one. Trust me that'd look roughly right, they'd burn a few guys and then probably die. It'd be cool.

Violet Fire - Pretty much a straight copy of the banish to inferno spell

So all 6 Tzeentch spells are actually doable, which is nice.