As the yellow colour was easily "soiled" by other dye stuffs, it more and more was associated to disgust, as colour of pus and of leprosy. A yellow flag on a house showed that the plague was raging there. According to the old faith people saw the cause for any trouble in the gall. A yellow coloured skin was a symbol for trouble, everlasting envy, jealousy and stinginess. In the Christian imagination envy and stinginess were two of the seven mortal sins, which constituted one more cause to discriminate the colour yellow. A negative culmination happened during the Nazi regime, when the Jews were forced to wear a yellow star on her clothes as badge. But the history of the discrimination and terror against the Jews is considerably older. During the 12th century the Jews had to wear a yellow hat.
Actors avoid the colour yellow and in theatres the curtains must never be yellow, as this is said to cause misfortune.