Complementary Colours

Definition : 

Complementary colours are two colours located on opposing sides of the colour wheel.  As a designer it is important to know which colours are complementary to another this helps to make good colour design based decisions. For example using complementaries can make an aspect appear brighter, they can also be mixed with hues or blended together to create shadows. In the most basic form complementary colours are both primary and secondary colour. 

The first set of complementary colours include: 

Yellow and purple 
Blue and orange 
Green and red 

By adding tertiary colours - made up of one primary and one secondary colour. These colours can be complementary: 

Yellow-orange and blue-purple 
Orange-red and blue-green
Red-purple and green-yellow 

Complementary colours are also made up of warm and cold colour such as yellow and blue. This creates simultaneous contrast, these are the highest possible contrasts available on the colour wheel. This occurs due to a natural illusion when you place tow complementary colours next to each other so colours will appear brighter. You may also choose to blend a complementary colour to a main colour to create a dynamic shadow. Complementary colours can also be used to make a hue less vibrant the more the more neutral a colour becomes. 

Colour Wheel 

Wheel demonstrating complementary colours