What sort of red carpet event could bring Nicole Richie, Rachel Zoe, and Kourtney Kardashian out to the valley? Turns out, it was just a pal's bday bash!

On Thursday evening the ladies, along with Courteney Cox and several other non-famous friends, attended Sara Foster's birthday party at Casa Vega in Studio City. Rach posted a picture from their table and wrote, "I love this gorgeous birthday girl @iamsarafoster #happybirthdaysara #ageless #hotmamma #greatfriends XoRZ." In case you didn't know, Sara is the sometime actress/daughter of music producer David Foster, and her younger sister Erin frequently hangs out with this clique as well.

Kourt looked fantastic (it still blows our minds that she gave birth to her third child just two months ago!) and while we love Nicole's outfit, her faded pink tresses seriously make us want to hurl. What's wrong with a natural hue? She looks totally hot with brown or blonde locks, so we don't understand why she's wrecking her remaining 90 strands of hair with all sorts of chemicals. And those roots?! They're almost as bad as driving the wrong way on the freeway in the middle of the night...