Vanessa Bryant -- Taps 'Project Runway' Designer ... For Xmas Card Dress

Vanessa Bryant takes her Christmas card photo VERY SERIOUSLY -- so seriously in fact that Mrs. Mamba tapped one of the top designers from "Project Runway" to make her dress.

Kobe Bryant's wife called upon MTCostello -- who has designed clothes for huge stars like Beyonce and Ariana Grande.

They got together and picked out MTCostello's signature "Black Widow" gown -- which comes with a $6,500 price tag!!

Vanessa had flirted with a bronze version of the dress during an earlier fitting ... but ultimately, decided to go with black.

Sources close to the situation tell us ... Vanessa has always been passionate about Xmas cards. As one person put it, "She takes great pride and puts great thought into celebrating because she's very religious."