From Wikipedia.
Lady Henrietta's dress has three layers - a white chemise, a blue under-layer, and a white satin surface layer with attention paid to discretely showing the blue satin layer. The resemblance of Lady Henrietta's dress with those worn by the Blounts is uncanny.
Keywords: 1735, Jervas, Henrietta Godolphin, Henrietta Pelham-Holles, Godolphin family, Pelham-Holles faily, Duchess, British, long straight coiffure, scoop décolletage, chemise, modesty piece, cuffs, criss-cross bodice, under-dress, three quarter length close sleeves, cuffs, natural waistline, full skirt