Unlike Audrey Hepburn, Grace Kelly's name is not so closely linked to black dress. We can remember her in icy blue, minty green, pure white or even fire red, but not so much in a black dress. The two most famous black dresses she wore on screen are the one she wore in films The Country Girl(1954) and Rear Window(1954). Both films were released in the same year, and both black dresses are of the same style: V neckline, cap sleeve, flared skirt, and Grace Kelly wore the two dresses with the same accessories: pearl earrings and necklace.
That seems to be her favorite style of black dress, which she since then carried in her private life in different versions. The most publicized black dress Grace Kelly wore off-screen was in 1955, on Cannes Film Festival. It was the same silhouette, again with V neckline and flared skirt, again worn with pearl necklace. She was then still with French actor Jean-Pierre Aumont. Just a few days later, Grace Kelly met Prince Rainier of Monaco. A year later, she was married to him.
After becoming Princess of Monaco, the few black dresses she carried were of slimmer silhouette, mostly column shape, and the neckline became higher. But she still wore the pearl necklace with the black dresses, sometimes.