From the 17th-century until around the 1770s only aristocrats were entitled to have red heels on their shoes, as a status symbol. Buckles were the most common type of closure, but ribbons laced through holes in the lappets were also used. Most were constructed of fabric on a wooden sole, but in the 1770s again, kid leather became increasingly popular. Heels after the 1760s became narrower and higher, while retaining the Louis shape, which flared at top and bottom, and curved sensuously in the middle.
In the 1770s and 80s the top of the shoe began to curve upward, creating a profile that looked as if the foot were being arched up out of the shoe. As hemlines rose with the Polonaise and similar fashions, shoes were increasingly seen, and assumed more variety in materials. Towards the end of the 1780s heels began to lower, and be forced inward under the foot more. Some slipped on without the use of lappets or laces, paving the way for the low slippers of the Directoire period.
One style that shows up again and again in paintings is the mule. A backless, slip-on shoe that research suggests was only worn indoors, or in the privacy of a residential garden. They originated in France and could be either formal or informal. Impractical, due to their tendency to slip off the foot, they exemplified the frivilous nature of many eighteenth century styles. For some truly wonderful examples of mules, and eighteenth century shoes in general. I refer you to The Bata Shoe Museum website (http://eng.shoe-icons.com/museum/objects.htm?age=41&page=1).
For anyone interested in modern reproductions of eighteenth century shoes see either of the sites below.
Sarah Juniper Shoes http://www.sarahjuniper.co.uk/18c.html
Plantagenet Shoes http://www.plantagenetshoes.freeserve.co.uk/home.htm