I'm such a makeup fan (to enhance, not overwhelm). I look closely at Princess Mary's makeup, since we have the same coloring, and try to take some cues from her. Her makeup is gorgeous, quite simply. I've wondered if she does it herself, or if she has help.
I've noticed her eyes are always made-up (never in black though, too harsh) with browns and grays, some shimmery shades. She wears a highlighter around the eyes/on the cheeks too it looks like in some pictures.
Her lips are always glossed in a light nude-pink shade during the day. I've rarely seen her in red/dark lipsticks. Light shades that reflect light are supposed to be the least aging.
It helps that her skin is flawless, she wears powder and most likely a light foundation but its not heavy at all. Her blush is usually peachy-pink, more peach than pink. Lastly, flawless brows frame it all.