For more info head to this video where you will watch a video showcasing the color powers system.
So remember the in this game you can use your brush to absorb different colors in the game. Colors are found in the "color cores". You find color cores when you defeat enemies. And when you touch or hit these cores they splat color in the floor.
You can then absorb the color by going over the paint and holding E over the it.
Once you have absorbed enough color you will be able to use the COLOR ATTACK. Each color you find has an unique attack.
As you absorb colors... they combine on the fly so you can combine colors to form new color attacks. For example, combining red and blue gives you purple and it's special color attack.
So the more colors you find the more combinations you have :) This allows for a lot of different possibilites in combat and different attacks.