From Zelda Legends Wiki
The Evil Orb is the boss of the Color Dungeon in The Legend of Zelda: Link's Awakening DX. It has no attacks, it just wanders around the room. However, its surface is very bouncy and will knock you back if you hit it with your sword. In order to defeat it, you must hit it several times in a row to make it change color, from blue to yellow to red. Once it is red it is almost dead. If you do not hit the Orb with your sword it will change back to blue.