The “First Era” of Regency, technically 1794-1804 (although there were “crossovers” from earlier & later styles), emphasized ancient Greek & Roman fashion.
This incorporated the “Little White Dress” of the draped statues, “Chemise a la Reine” that Marie Antionette had introduced when she escaped to her “Petit Hameau” to wear what was basically her underwear, & the ideas brought from Indian and West Indies fashion by Parisiennes living abroad.
Combined with the availability of the white muslin fabric, new rinses for keeping white clean, & the influence of ideas regarding simplicity & the “country life”.. women around the world embraced the style…
… until it got a little chilly..
(sketch: 1st Regency Era women dress as early Greeks & Romans at home & at formal occasions)