Julia Roberts "never gives direction" to her hairstylist and makeup artist.
Genevieve Herr has been doing the 47-year-old actress' red carpet make-up for over a dozen years, and has revealed Julia has absolutely no input when it comes to her hair and face, allowing the "experts" to do their work.
The make-up artist said: "Julia never gives directions. She says, 'You're the experts,' and she sits there and is 100 percent all ours."
Genevieve - who has also worked on actress Katie Holmes - revealed Julia is "always laughing", and, with this in mind, opted for "fun" pink lips when it came to the Lancome ambassador celebrating the beauty brand's 80th birthday in Paris.
She said: "Julia is always laughing, so I try to keep her makeup fun because that fits her personality."
For the special day, Genevieve also used a weightless foundation, due to the 'Pretty Woman' actress being "older", as well as a shimmery pink blush, and Julia was "really happy" with the finished look.
Genevieve added to People magazine: "It's important to use lighter textures as you get older. I usually use peach (blush) but I said, 'It's a party, it's festive, let's give you a little more blush.'
"She was excited! She said, 'Oh my God, I look great, thank you.' She was really happy, and she looked amazing from head to toe."