The Colour Wheel
To be able to make an informed decision about the right colours to put together you need to have a basic understanding of colour principle. A good place to start is the colour wheel.
The most basic colour wheel contains three segments, each containing one Primary colour; red, blue or yellow.
Divide the wheel down to six segments. The three Primary colours are positioned an equal distance apart and in the segments in-between a colour is made from both the combination of both surrounding colours. These are the Secondary colours; purple, green and orange.
Divide the wheel down even further to 12 segments. As before all six colours (Primary and Secondary) are positioned equal distance apart, and in the segments between, a new set of colours are made from a combination of the two surrounding it. These are the Tertiary colours.