How do I cover up the color of my macbook?
This YouTube video uses the

air-dry, specialty rubber coating. In fact, it's the original peelable, flexible, insulating, non-slip, durable rubber coating

Plasti Dip® to color the macbook black.
You have to clean the macbook very well before application, and you will have to mask every key on the keyboard, the screen, and your ports of course. Be careful.
The YouTube video says

you're going to want to let it set for at least 24 hours out of direct sunlight in a room that is room temperature

I'm sure you can find other colors of air-dry spray-on rubber coatings.
Obviously the downside to this method is that your Macbook will no longer feel like metal, and will not look like metal either.