To appreciate red, I find it helpful to have a basic understanding of colour.
Colour is light (or as Johannes Itten puts it, “colours are the children of light, and light is their mother”).
When light hits an object, the object will absorb the wave lengths of light which are most similar to the atomic structure of that object – the remaining wavelengths will bounce (reflect) into our retina and we perceive it as colour.
Red has the longest wavelength in the spectrum – a bigger job for our brains to de-code. This de-coding can actually increase our pulse rate which is why designers use it if they are wanting to create a stimulating environment. It has also been known to increase ones appetite, possibly why it is often used in dining rooms.
Due to its long wave length it appears to “advance” towards us – in other words it feels closer because its wave length is long and reaches out towards us. This is precisely why it can make a room appear smaller. This effect can be used to your advantage. If for example you have a long narrow room or corridor, you can paint the short walls red. The advancing nature of red makes the far wall (short wall) feel closer thus “shortening” the long walls.
A useful tool indeed.
Photo taken at Tent, London Design Week 2010.