Color theory encompasses a multitude of definitions, concepts and design applications and there is lots of information out on the Internet. You will find studies of colour theory in art and design, Phycology and the emotional association, and science with the breaking up of light into measurable frequencies. All these fields help us understand colour and its application.  
In the following slides you will find useful information on: The color wheel, color harmony, and the context of how colors are used.

Colour Theory Page 2: looking at Tints, Shades, Complimentry colours and its applicaction.