Yellow itself is a warm colour, and a highly visible colour making it useful for hazard signs and emergency vehicles. This colour tells of happiness and joy yet cowardice and deceit.
In Egypt yellow is the colour of mourning, and interestingly, actors in the Middle Ages wore yellow to signify the dead. For Japan, yellow represents courage, in India this colour is of merchants and in China yellow is the imperial colour.
Yellow is also the colour of the 3rd chakra known as the Solar Plexus, yet also at the same time associated with the element of fire and such things as wisdom, joy, happiness, enlightenment and optimism.
Yellow has been used to indicate honour and loyalty yet people see yellow as the colour of cowards. Dull yellow itself represents such things as caution, sickness and jealously.