Entertaining fire

Once cast creates a 15 foot square of flames centered on the target. The flames cast by this spell is a rainbow like-color and seems to dance as the target is damaged.  Target creature cannot escape spell. Spell lasts 2 rounds. The spell starts out with 1d12+4 damage at first level, at third level spell damage increases to 2d12+5 damage. At fifth level damage increases to 3d12+6, at 7th level damage goes to 4d12+6 and finally at 9th level damage is 5d12+8.