Another factor is that a significant number of people suffer from colour blindness, an inability to distinguish one or more of the colours red, green and blue. The most common is protanopia or red-green colour blindness followed by tritanopia or blue-yellow blindness.

Those who suffer from deuteranopia have trouble seeing green. This inherited sex-linked disorder affects 20 times as many men as women; studies suggest up to 10 per cent of all men have some degree of colour blindness.

Colour science

Aside from the symbolic values associated with certain colours, many societies have different associations. For example, Europeans tend to associate white with purity and cleanliness whereas Asians relate it with mourning or death. In the west, red is seen as wanton, but in Asia it is perceived as pure or lucky. So wearing a white or red wedding dress will cause misunderstandings at an international ceremony. We also learn new associations; if you have enough happy times in a black environment, you will eventually link this colour with partying - even if your upbringing is western.

Despite individual and cultural differences, evidence suggests many people share similar reactions to particular colours. Warm colours that encompass hues from red to yellow, including orange, pink, brown and burgundy, tend to excite. Their opposites, the cool colours with hues from green to violet, including blue and all the shades of grey, slow down the body's metabolism.

Experiments have shown that rooms painted in warm colours are often perceived as hotter than rooms in cool colours. Also, time seems to pass slowly and objects seem longer, larger and heavier under a red light; the exact reverse is true under a blue light. Light rooms seem larger than those painted in dark colours; even bottoms seem smaller in dark jeans than light jeans. To take this analogy further, a black suitcase is perceived heavier than the same one in white, so carrying the black one appears to tire you more than the white suitcase even though they are identical.

Of the warm colours, studies have shown yellow, especially pure bright lemon yellow, is considered the most fatiguing colour. Physicists say this is because bright colours reflect more light; bright shiny yellow overstimulates the eye very quickly. It may be an ideal colour for an eye-catching Post-it note, but babies cry more in yellow rooms, husbands and wives fight more in yellow kitchens, and opera singers throw more tantrums in yellow dressing rooms.

Of the cool colours, blue is considered cooling and calming when on a wall or in nature, but not on a plate. Sapphire foods trigger a subliminal alarm button that suppresses the appetite; you may love the idea of blue jelly and Smarties, but our brains know very few natural foods are this colour. So if you're trying to lose a bit of weight, putting food on a blue plate or pasting a blue filter over the refrigerator light will help.

Healing Colours

Doctors in ancient Egypt, China and India bathed patients in colours of light specifically chosen to heal various ailments. Today's New Age practitioners suggest that as light flows through our eyes it triggers hormone production, influencing our body's biochemical system.

Modern therapies recommend red as a liver energiser, orange to strengthen the lungs, green to relieve tension, and yellow to boost the alimentary tract's functions. The stronger and purer the colour, it is said, the faster and greater the effect. Some practitioners believe that simply visualising a particular colour can have an effect.

Critics say that as colour perception is not universal, effectiveness will be highly individual at best. As few empirical studies of this therapy have been carried out, it is hard to say how effective this remedy is.

If you feel energised by red and calmed by green, it makes sense to use those colours in your environment. But if you have a health complaint, be safe and visit your doctor.