The answer is D. You know that thing that goes Do Re Mi Fa So La Te Do? There’s a good chance you sang it in your head. It’s a scale :)
Different colors express different moods, for example we often associate red with anger, blue with sadness. So the color can affect the mood set for you artwork. Also, in like abstract drawings it can help you because we often associate colors with certain landscapes.
I feel like this is what my brain thinks of when it's post to be productive