Check the links through to the Orders on
http://wh40k.lexicanum.com/wiki/Orders_Militant for sample models.
There are six 'Major Orders' (roughly equivalent to First Founding Legions), the traditional poster army is the Order of Our Martyred Lady (black armour, red cloth, white hair) and the Order of the Sacred Rose (white armour, black cloth lined with red, black hair) featured in Dawn of War.
They've all got a red/black/white palate with metallic accents, I suspect this may change with the introduction of the new models/Codex because some are hard to tell apart at a glance.