Pea soup was usually made from dried yellow split peas, not green ones…

The Illustrated London News, Volume 10, January to June 1847

From The Washington Post:

During the Victorian era, the worst London fogs occurred in the 1880s and ’90s, most often in November. Yet as early as 1853, in the opening pages of “Bleak House,” Charles Dickens refers to “implacable November weather” and goes on to describe “smoke lowering down from chimney-pots, making a soft black drizzle with flakes of soot as big as full-grown snowflakes — gone into mourning, one might imagine, for the death of the sun.” There is, he says, “fog everywhere” — and not the soft, dove-gray cloudiness we might imagine: This was 19th-century air pollution: thick, malodorous, yellow or black and almost smothering.

As Christine L. Corton reminds us in “London Fog: The Biography,” England’s capital “has always been susceptible to mist and murk.” As early as the 17th century, the diarist and gardener John Evelyn was complaining about the increasing “smoke” problem, blaming lime kilns for poisoning the atmosphere. By the time Queen Victoria came to the throne in 1837, dense fogs could make travel, whether by foot or horse-drawn carriage, almost impossible — and the adverse conditions could persist for days. An 1892 study concluded that between 1886 and 1890 there were, on average, 63 foggy days per year. During these periods of stygian gloom, “linklighters” — street urchins carrying homemade torches — would guide gentlemen and their ladies through the darkness for a charge. Sometimes, the well-to-do would be led helplessly into alleys and robbed.

London’s fogs mostly resulted from the gritty smoke of domestic coal fires and “the noxious emissions of factory chimneys,” coupled with the right atmospheric wet and stillness. Sulfurous elements gave the resulting miasma a yellowish tinge like that of pea soup (then usually made from dried yellow split peas, not green ones). A bad fog was consequently “a pea-souper” or, later, “ a “London particular” (originally a term denoting a kind of brown Madeira wine). Besides yellow and brown, fogs were described by Victorians as “gray yellow, of a deep orange, and even black.”

““London Fog,” a study of the great city’s legendary atmosphere”, Michael Dirda, The Washington Post