What key is Carol or Winter Peace in?

What is one of the most effective ways that artists create space in two dimensional art?

Acurious child asked his mother: “mommy, why are some of your hairs turning grey? ” the mother tried to use this occasion to teach her child: “it is because of you, dear. every bad action of yours will turn one of my hairs grey! ” the child replied innocently: “now i know why grandmother has only grey hairs on her head.”

Name the primary colors. why are these colors considered the only “primary colors”?