Anglo-Saxon, geolu, yellow; Italian, giallo; Danish, guul; Icelandic, gull, our gold, yellow metal.
Yellow indicates jealousy, inconstancy, and adultery. In France the doors of traitors used to be daubed with yellow. In some countries the law ordains that Jews be clothed in yellow, because they betrayed our Lord. Judas in mediæval pictures is arrayed in yellow. In Spain the vestments of the executioner are either red or yellow- the former to indicate blood-shedding, and the latter treason.
Yellow, in blazonry, is gold, the symbol of love, constancy, and wisdom. Yellow, in Christian symbolism, also gold, is emblematical of faith. St. Peter is represented in a robe of a golden yellow colour. In China yellow is the imperial colour.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894