MidnightStudio - Page 19

Yellow is a joyful, happy color. It is "an unstable and spontaneous colour. It has many different meanings, both positive and negative, and this may be why we use yellow as a sign of caution between red (danger! stop!) and green (safe! go!). Yellow seems to be a compromise, a middle way, between positive and negative..." (http://symbolism.wikia.com/wiki/Yellow)
It can also be seen as a sign of aging or ancientness. (e.g. old, yellow papyrus, old, yellow, brittle bone, etc.)
It can also stand for falsehood, unreliability, and cowardice.
It can be a symbol of summer.
In ancient China, it was associated with soil (of the five elements) and was a sign of royalty, as the royal family was supposedly descended from the sun and possessed the exclusive right to wear yellow.
Gold yellow represents illumination, wisdom, or high quality.
Dirty yellow represents age and decay.
Light yellow represents intellect, freshness, and joy.