YELLOW
It's a warm colour with conflicting symbolism that signifies joy and happiness as well as cowardice and deceit. Due to it's visibility it's often used in warning and emergency signs. It represents danger although not as strongly as red.
Cultural Symbolism
Western: joy, optimism, happiness, hope, sunlight, wealth, idealism, Summer, liberalism, cowardice, hazards, dishonesty, greed, quarantine
Eastern: royalty, mourning (Egypt), courage (Japan)
In combination with other colours:
Blue - adding yellow creates a good contrasting scheme
Orange - adding yellow gives you a healthy, summery, fruity scheme
Green / Brown - adding yellow gives a sense Autumn
Black / Grey - adding yellow creates a high-tech look