Nicole Richie's Met Gala 2013 ensemble was "sick" -- in a good way, according to Rihanna. Though the 25-year-old "We Found Love" singer and designer had to miss the Met Ball due to her concert in Boston on Monday, May 6, she kept an eye on the red carpet arrivals and picked a favorite.

"This bitch makes me throw up!" Rihanna tweeted about a photo of Richie. But the "Unapologetic" singer apparently meant it as a compliment, adding in a hashtag, "Best Dressed. 2013 Met Gala. Nicole Richie." 

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The Fashion Star mentor, 31, walked the red carpet at the Costume Institute Gala in New York City Monday wearing a long white Topshop dress with a floral pattern. To go with the punk theme of the evening, Richie dyed her hair gray-blue and styled it in an updo.

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"We wanted to look to be an elevated, next level kind of punk," celebrity hairstylist Luke Chamberlain told Us Weekly. "Something that could hold up to her incredible, collaborative Topshop dress."

To get the look, Chamberlain took small sections and "applied the hair paint using a tint brush." Once the color was distributed, he "secured the style using white hair pins." 

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Richie also made Us Weekly's 2013 Met Gala best-dressed list. Tell Us: Did you think her punk rock ensemble was "sick?"

Click here to view the live stream (+ archived version) of the 2013 Met Gala on

This article originally appeared on Rihanna: Nicole Richie's Met Gala Ensemble "Makes Me Throw Up"