10 Downing Street A view of the door to number 10 Downing Street. Photo by Dan Kitwood/Getty Images

The black exterior of 10 Downing Street, where the British prime minister lives and works, is famous worldwide.

But the iconic black facade was not always this colour. 

During extensive renovations to Number 10 in the 1960s, workers discovered that the bricks were actually yellow.

Hundreds of years of heavy pollution had stained the bricks black.

"To keep the familiar appearance, the newly cleaned yellow bricks were painted black to match their previous colour," according to the 10 Downing Street government website.

Number 10's famous black front door has also been updated in the last two decades. The original black oak door was replaced with a bomb-proof metal one in 1991, after an attack by the Irish Republican Army in which a bomb exploded in the garden. The new door is coated with a high-gloss paint, which keeps it incredibly shiny.