Colonial fashions were worn in the late 1700s. This would be the Georgian period (named from the reign of King George III), but colonial focuses more on the the American Revolution era, which is the setting for the Felicity American Girl series. Fashions during the French Revolution (as in The Scarlet Pimpernel or A Tale of Two Cities) are similar. The dresses started changing to Regency styles in the mid 1790s.
Felicity Merriman and her best friend Elizabeth Cole are the American Girl dolls from this category.