This power is always my answer to the "what power seems useless but is actually overpowered" prompts.
It seems dumb, but imagine being able to mark your enemies in day glo orange on a battlefiled, or to cause confusing and vertigo by strobing colors at people, or camouflage your team to perfectly match the surronding environment. Imagine an artist walking through the world throwing 40ft murals up at a whim.
On the evil side, you could cause all sorts of fatal accidents by blanking the world white suddenly, or write threats 10 stories high on buildings in letters in any color you like. You could ruin every person's outfit around you at a moments notice. You could bring whole industries to their knees by just fucking with color. Walk into a kroger and turn every item on the shelves, all of it, puke green or blood red. Just roll around the world, causing confusion and ruin.