Discordant Colours

A lot of optical illusions often use an interesting choice of colours, normally on opposite sides of the colour spectrum (discordant colours), found a couple of websites talking about these  colours and how they work within design etc.
http://ruoloc.blogspot.co.uk/2009/10/discordant-colours.html
http://ginva.com/2012/04/why-colour-clashes-work-in-design/