We don't know what's more jaw-dropping: Kim Kardashian's boobs or her little sister Kylie Jenner's roots!

The ladies attended Cosmopolitan’s 50th Birthday Celebration at Ysabel on Monday in West Hollywood. While Kris, Kim, Khloe and Kourtney wore all black, Kylie just had to stand out from the crowd, rocking a white outfit -- and some seriously bleached locks! “I didn’t get the ‘wear all black’ email,” Kylie wrote on Instagram, adding that the blonde hair was "just for the night.”

Phew! We were worried for a second there...

Kim, who is seven months pregnant with her second child, was practically busting out of her bodycon dress, which she paired with a $3K Balmain choker. Of course Kimbo's dress was see-through under the bulbs and all eyes got a glimpse at her bra. The reality star really should know better -- she's worn that black tube sock of a dress enough times during this pregnancy!

After the bash, the gals all went to West Hollywood hotspot Craig's because one glamorous event just isn't enough for the Kardashian/Jenner klan ...