I like the idea that you "subtract" a color that is inside of you to light the world and that your current color is a hint what other colors you still have. The issue I had is that that was not what I expected. I thought that my character is more like a color-changing lightbulb. Because of that I was confused that character had different color than the one I used to light the world up.
An idea came to my mind of how you can introduce that mechanic without confusion step by step. You can make the player start with single color and give a hint how to use that color. After that you could spawn a color ball to show the player that colors can be recharged. After second use of the same color you could spawn a ball of another color and show how to use this one. You could repeat it with each color separately, and after that you could spawn balls of two different colors and show how the body color changes when consuming them and after using each color. You could again do that twice for each pair, so that the player can test each combination. After that you can introduce white by giving the player balls of three different colors. And using white would lead to finishing the intro level.
Good point with issue of fitting the pattern on small items. First thing that came to my mind was - do they have to be small? :D If yes, than some solution would be needed for that case. But I know that sometimes it is easy to fall into fixing problems created by some specific solutions (like making some elements small), while changing the solution is the easiest way to not have the problem in the first place. ^^