Obviously, none of the above mentioned clothing would be any good for a grand soiree or rout. For an important haut ton event, something truly special was required.
Unlike afternoon dress, for evening it was quite proper to show one's bosom. Indeed, some bodices were so low they were in danger of showing even more. Wide scoop necklines were popular for evening wear, as were low squared necklines and low bodices cut straight across. In some paintings of bodices of this type, it's hard to imagine how the sleeves even attached.
evening gown For evening wear, light fabrics were still favored, but they were richer. Very fine muslin, silk satin, duchesse silk and light taffetas were all popular. Braver, older or married women sometimes wore silk velvet. There was an unspoken dress code for debutantes, which applied as much to evening wear as afternoon dress. Young ladies were expected to wear pastels and white. The more sophisticated, darker colors were off-limits to unmarried misses just out of the schoolroom.
Of course, it's important to remember that dark colors would not show well by candlelight; if one wore black, one would likely disappear! To this end, many dresses utilized metallic trim and glass or crystal beading to catch the light. Short sleeves were often seen in evening dress, but long gloves were a necessity. Above-the-elbow was the preferred length. We often think of gloves as either white or black, but many different colors of kid leather were used, including yellow and blue.
Outerwear for the evening included cloaks, capes and shawls. To my knowledge, spencers and pelisses were never worn with evening dress.
http://www.rakehell.com/article.php?id=387&Title=Introduction-To-Regency-Dress
