Bianca Censori covered up for a day at the spa ... masking her face with a shirt -- while basically letting her boobs hang out!

Check out the clip -- Kanye West's wife enjoyed an afternoon at a salon spa in L.A. Saturday ... and when she left, photogs had plenty to snap photos of thanks to her sheer boysuit.

Censori puts a shirt on over her face -- channeling her husband's oft-used look -- but the sheer nature of her outfit leaves no part of her chest to the imagination.

Unclear why she got camera shy suddenly ... photos taken earlier in the day show she didn't feel the need to wear the shirt on the way in. Kanye was with his wife ... sitting in the passenger seat of the car.

This outing came only about 12 hours after the pair supported his daughter, North, at her pop-up in Los Angeles dedicated to her new EP "N0rth4evr."

The two wore matching fake face piercings ... and Complex -- which collaborated with North on the event -- reported Ye signed autographs and took pics with fans.

North's famous mother, Kim Kardashian, went on night #2 Saturday ... so no awkward interactions between Kanye's ex-wife and his current wife.

After a long night out, it seems Bianca got a chill day at the spa ... and fans got another one of her head-turning looks!