A color change, while able to be used as a magic-effect on it's own is considered a sleight, merely a tool of magic used to create an effect. Just the same way, wooden planks and nails are tools to create a house, but not a house on their own. But it depends on the way it's presented, just like always said, magic happens in the mind of the spectator, not the hands of the magician. If they don't consider it magic, then it isn't.
A color change is a tool to create magic, which has a magical appearance. As simple as that.