Colour Wheels - A collection of colours arranged together that compliment each other. They can be a set of primary colours, secondary colours and complimentary colours.
Colours are a key aspect when designing websites, take a look at this site
The multicoloured moving background is so distracting and makes the user want to close the website rather then take a look around the site.
Colour can also represent moods, it is believed that certain colours can affect the behaviour of people.
Red - Anger
Blue - Down/Upset
Green - Envy
Yellow - Happy
Although some colours do represent moods in certain cultures colours can represent different emotions such as white in Christianity represents virginity however in Hinduism it represents death.