Inexpressibles, what were they, you ask? Very very tight, usually knitted of silk, trousers–almost like today’s women’s leggings, designed to show off a gentleman’s muscular legs to best advantage. They were also known as bum-clingers and the term inexpressibles said it all–for what respectable woman could express that?
In colour, they tended to mirror that of a classical Greek statue–pale greys, pale ochres like sandstone or marble. Because that was the whole idea of the thing, or the look, if you prefer.
The tight buckskin breeches, or inexpressibles of a pale colour, when worn with the tight waistcoat also of a pale colour were meant to create the impression–should one see the wearer without his coat–that you were viewing a naked Greek god or hero carved out of stone or marble with his enviable godlike physique. Make no mistake, it was highly erotic. And they meant it to be.
Then, depending upon how his crown jewels fell most comfortably, a gentleman’s breeches or inexpressibles were cut with extra room in one of the thighs, so that everything lay neatly (or not) down along the one side. Though given the fabric and cut of these garments there were very few secrets.
Another innovation of the inexpressibles, and this was added by Beau Brummell–to whom we also owe the fine practice of daily bathing–was a strap under the instep of the foot, which kept the trousers firmly down inside the boot. He brought this in because cavalry breeches had had these straps for years–just as many breeches and jodhpurs still have–and he had been an officer in the cavalry. So not just a pretty face, ha ha.