The Over The Rainbow team discuss the colour yellow. Yellow Ochre was one of the earliest pigments used by mankind. Orpiment was also widely used in antiquity despite it being based on arsenic and being poisonous. Yellow has also long been an important colour culturally. The Greeks – starting from Empedocles – believed that the world considered of four elements; each of the elements was associated with a colour. Yellow (or a yellow-green colour) was associated with earth; white with air, black with water and red with fire. This tetradic thinking about 4 special colours continued until the 14th or 15th Century; the idea of three special colours is a relatively recent idea. Yellow is probably the least favourite colour and invokes quite different reactions in different people. It is, perhaps, the marmite of colours.