The way that premium hairstyles have two recolours is awesome.
Heraldic/Max/Comp cape recolouring is even better.
Many outfits would clearly benefit enormously from being able to be recoloured similarly.
I would wager a great deal that quite a few of the fashion-interested community would willingly re-purchase outfits they already own even at a higher runecoin price if they could do a more intricate recolouring job.
Food for thought. And if you ask me, extremely untapped potential for extremely low time/effort investment on Jagex's part.