The color yellow has varied meanings and connotations. It is simultaneously associated with optimism, sunshine, joy, caution, cowardice and decay.
Bright yellow reflects a high level of light and is therefore highly visible (in the form of taxicabs and warning signs) and is thought to be energizing.
Dull yellow, however, fades against white and becomes dingy, recalling deterioration and sickness.
“Yellow bellied” “Yellow Journalism” “Follow the yellow brick road”
“[…] what we term the substance of each color is neither the active nor the passive element, but something which passes between them, and is peculiar to each participant; are you certain that the several colors appear to every animal — say a dog — as they appear to you?” — ‘The Pythagorean Theory of Music and Color” in The Secret Teachings of All Ages by Manly P. Hall (1928)