Colour

The Silhouettes were allergic to colour. (COMIC: Sunscreen)

In the America, from at least 1943 to 1956, people who were classed as non-whites or of a colour were segregated from several places in states like Alabama. For instance, coloured people were segregated on the bus services, forced to sit at the back and get on through a side entrance while whites could get on the front and sit there. Also, coloured people were forbidden from staying in whites-only motels like the Sahara Springs Motel and were refused services at diners. (TV: Rosa)

Mrs Smith's boarding house had a "no coloureds" sign, much to Ace's disgust. (TV: Remembrance of the Daleks)