"She has made some really beautiful changes in her life," Barnes, who first met Markle shortly before production on Suits began, told ET's Lauren Zima. "What I would say though, her core self is there. That's not going to change, it's only going to open up and flower."
"I think some people thought it would elevate and become stronger, but I think it's become more subtle, more nuanced," he added. "She's kept that understated, refined, sophisticated quality, and I like that about her. She hasn't become a totally different person. She's consistently been her, and I think that's been fun to watch."
"I don't think she's a person who naturally wants or needs or feels like she has to put on a lot," Barnes gushed. "She's softly defined, and that's when she shines her brightest and looks her best. When you're seeing freckles, and you're seeing some of the natural qualities of skin, it's a good indicator that there's very little on there!"
"My philosophy has always been, and one of the things I'm known for as an artist, is helping people achieve beauty with products that help bring out their features," he continued. "I can paint, I can do full glamour, but I think when people say, 'Wow, you look stunning,' versus, 'Wow, you have really beautiful makeup on,' there's a big difference in that kind of a compliment."
Although Barnes admitted he hasn't seen a lot of Markle since "she went off to London" to be with Prince Harry, he'll never forget the times they've worked together. Back when he was still doing her makeup, he says Markle always requested a natural look.
"She loves beautiful skin, to start with, and she has the most gorgeous complexion," he gushed. "It's that soft, caramel. Her mixed heritage makes her an exotic beauty of beauties. Her chocolate eyes, the way her eyes light up when she smiles, I love her smile, her teeth and her lips. And then her perfect brows."
"Whenever I'd work with her, she'd like to highlight her fresh, radiant skin," he continued. "We'd do a very glowing, fresh-faced skin. We'd use earthy tones, colors that enhanced her natural beauty, rather than a lot of obvious color choices, like purple, green or blue. We'd stick with earthy tones -- peaches, golds, browns -- a lot of rich, warm tones and that really flattered her. It helped her just look radiant and fresh."
Barnes, whose celebrity client roster also includes stars like Julianne Hough, Nina Dobrev and Laura Prepon, said he never went with heavy makeup for Markle, simply because "she didn't really need it."
"We did [a red lip] once on a red carpet," he recalled. "It was really fun and she got a lot of attention for it, but typically, she'll wear nude or a peachy nude."
As we patiently wait to see what type of makeup Markle will wear for her May 19 nuptials, watch the video below to hear more on her evolving beauty and fashion. And be sure to keep up with all of ET's coverage of the royal wedding as we count down to Markle's journey to the altar!