Mansel, Philip. Dressed to rule : royal and court costume from Louis XIV to Elizabeth II. (New Haven: Yale University Press, 2005).
Portions available online at Google books
My thanks to Judith Heidelbergensis for posting the Heideloff 'Gallery of Fashion' magazine plates in color (I only have the black and white so I'm linking to hers instead - much more lovely!).
Candace Hern's page on the New Hoop of 1817. See also her page on court dress: http://candicehern.com/regencyworld/court-dresses-overview/court_dress7b/
https://s-media-cache-ak0.pinimg.com/736x/16/b8/e2/16b8e2777119653195dbfe15027fdfbf.jpg
1812, July, Ackermann: "The train still continues short, except in court dress; and many wear the evening dress a walking length." p. 45
1794, July Heideloff: "Body and train of striped lilac and silver tissue"
https://s-media-cache-ak0.pinimg.com/736x/db/7e/05/db7e05cb24a6803ddafa66ec77ce3ad7.jpg
1795, Feb. Heideloff: "Body and train of carmelite silk velvet" http://40.media.tumblr.com/tumblr_lon9wbfixd1qga5wno1_500.jpg
1795, July: Heideloff "…train and body of lilac silk"
https://s-media-cache-ak0.pinimg.com/736x/76/a7/31/76a7314d9a4d7f5a688284edf1a18142.jpg
1796, Feb. Heideloff "Body and train of maroon and black striped velvet" http://world4.eu/wp-content/uploads/2013/02/Gallery-of-Fashion-Heideloff-0054-154x200.jpg
1796, July Heideloff "Body and train of lilac tiffany, spotted with silver" (the main
color of the gown and drapery is yellow)
https://s-media-cache-ak0.pinimg.com/736x/19/09/12/190912da566b641c6a2b0b309dec8e27.jpg
1797, Feb. Heideloff: "Body and train or purple satin, richly ornamented with gold lace"
https://s-media-cache-ak0.pinimg.com/736x/4f/eb/3b/4feb3b3f5ee335241f988fb34730fdcf.jpg
1797, July. Heideloff "Body and train of lilac crape" (no image)
1798, July. Heideloff "Body and train of light yellow crape, embroidered, like the
petticoat, with silver leaves"
https://s-media-cache-ak0.pinimg.com/736x/ea/20/d6/ea20d6af1aac63278581bd1e06f5b470.jpg
1799, Feb. Heideloff: "Body and train of damon-cut purple velvet, embroidered in
gold, and richly ornamented with fringe."
https://s-media-cache-ak0.pinimg.com/originals/a1/02/23/a102234c6f66bedb0b74b9f8017b691f.jpg
1799, July. Heideloff: "body and train of green silk, the train trimmed with
a silver fringe"
https://s-media-cache-ak0.pinimg.com/736x/b6/06/d9/b606d96bd73c114de08c91612b53d9fe.jpg
1800, Feb. Heideloff: "Train of purple satin, falling back at the shoulders,
and trimmed all around with rich gold trim"
https://s-media-cache-ak0.pinimg.com/736x/7a/6e/96/7a6e96f4efe9bca8160c41c444716929.jpg
1800, July. Heideloff: "Body and train of lilac sarcenet, trimmed round the
neck and down the breast with diamonds"
https://s-media-cache-ak0.pinimg.com/736x/64/d2/c9/64d2c9cbd769e6253c53a60f847f232e.jpg
1801, Feb. Heideloff "Body and train of rose-colored satin worked in gold…"
https://s-media-cache-ak0.pinimg.com/736x/26/25/f8/2625f86d722a980f59772a4e534ae41f.jpg