Although the colour black is the most common for London taxis, it is not a requirement. Taxis can be a variety of colours red, blue, pink, white, even green. In the modern-day many of them have even chosen to be wrapped in advertising from companies such as Sky Sports.

While the iconic "Hackney Carriage" is most famously known as the "Black Cab," London taxis can technically be any color. After World War II, the dominant taxi model, the Austin FX4, was produced in black as the standard factory color because it was the cheapest and most durable option. Over the decades, this became a tradition and a globally recognized symbol of the city. Today, while the vast majority remain black, you will frequently see London taxis wrapped in vibrant advertisements for various brands, or even painted in specific colors for special events, such as the silver or gold cabs produced for Royal Jubilees. Despite the exterior color, a vehicle must meet the strict "Conditions of Fitness" set by Transport for London (TfL)—including a very tight turning circle—to be licensed. Whether they are black, red, or covered in a movie poster, they are still colloquially referred to as "black cabs" by locals and tourists alike to distinguish them from private hire vehicles like Uber.