Pastel blue and muted green walls are a common feature in many hospitals around the world, and for good reason.
These colours are thought to have a positive psychological impact on patients, boosting their mood, stabilising blood pressure, reducing stress and anxiety and, in turn, speeding up their recovery.
Blue, the colour of the sea and the sky, is said to have a soothing, calming effect, while green, which is typically associated with nature and the outdoors, is thought to help patients feel more grounded and centred.
Colour therapy, also called chromotherapy, is not a modern concept. Ancient cultures believed that colour could help healing and improve emotional well-being.
In ancient Egypt and Greece, rooms were painted in different colours in an attempt to treat various ailments. The Egyptians even designed special healing sanctuaries that captured and split the sun's rays into its component colours, creating therapy rooms bathed in light.
Colour is also central to Ayurveda, a traditional Hindu system of medicine that originated in India thousands of years ago and is still practised today. Ayurveda uses the energy thought to be inherent in various colours to stimulate healing in the body's energy centres, or chakras. Each chakra is associated with a single colour of the visible light spectrum, along with a function and organ or bodily system.
Ancient Chinese texts, too, highlighted the use of colour to restore imbalances in the body.
The psychological effects of colour
According to Mille Sylvest, an architectural psychologist at 3XN Architects in Copenhagen, colours communicate with us on a sensory, symbolic and cultural level. Colour also shapes our reality because the objects around us stand out from one another through colour.
Sylvest says that warm colours, such as yellow, orange and red are thought to activate our sympathetic nervous system, which increases our blood pressure, temperature and adrenaline production.
Cool colours, such as blue and green, on the other hand, activate our parasympathetic nervous system, causing opposite effects.
Indeed, in a global poll conducted by paints and coatings company AkzoNobel, blue and green were associated with positive emotions and healing. The top trend colour for 2014 is a combination of both colours - teal - says the company.
Herlev Hospital in Denmark is one health care institution where patients are stimulated by well-lit, colourful rooms, says Sylvest. Decorated by renowned artist Poul Gernes in 1969, the hospital features a bold yet considerate use of colour, from the sunshine yellow doors to the striking blue floors and red walls. The rooms face different directions and the colours correspond with the type of natural light the rooms receive.
So cooler colours feature in the rooms facing north, while warmer colours are used in the rooms facing south.
White should be avoided in hospitals and health care institutions because it can cause sensory deprivation, says Sylvest. In Asia, white is also associated with death, mourning and illness. The AkzoNobel poll found that men connect this colour with fear more than women.
In Western countries, black is often linked to negative events and emotions we cannot control, such as fear, sadness, shame and disgust. It should not be used in places where healing and recovery take place.
Interestingly, the AkzoNobel poll found that red was associated with positive emotions (love and pride) as well as negative ones (fear and anger).
The theories of colour psychology should not be used indiscriminately, however. The overuse of colours can intensify problems. For example, the overuse of supposedly soothing colours, like blue and green, in mental health care facilities has been found to exacerbate depression in patients.
When using colour in places of medical care, other factors such as the size of the space, lighting, and position of the windows must also be taken into consideration, as these can affect how the colour appears or "behaves".
The light fantastic
Colour therapy is not limited to interiors. As energy waves, or light, colour can be used in the treatment of certain physical conditions and even improve emotional health.
Light is basically energy that travels in the form of a wave, and is made up of many colours. Every colour, therefore, is a form of energy, with each colour possessing its own frequency.
In chromotherapy, coloured light is shone or beamed onto the skin. Through this method, energy is "fed" to our aura, or energy field, and then transferred to our body. Our body recognises these wave forms and responds to them.
Different wavelengths of light (or different colours) are thought to have health benefits. Many health care practitioners administer coloured light therapy by way of lasers, lamps and LEDs. Over the years, many studies have been carried out to determine the most effective colours for treatments.
Doctors at Massachusetts General Hospital, for example, found that blue light, when beamed onto the bellies of patients, was effective at reducing the amount of Helicobacter pylori bacteria in the patients' stomachs by up to 99 per cent. Blue light has also been effective in the treatment of back pain, rheumatoid arthritis and acne.
In other studies, orange light helped with insomnia and balance problems; green light was effective in combating depression and healing wounds; red light targeted burns and hair loss; and pink light helped suppress aggressive behaviour.
The colour controversy
Despite its use in interior decorating and light-based treatments, colour therapy remains a contentious subject.
Dr Edward Shen, a registered psychologist at Matilda Medical Centre, says that colour therapy falls under the umbrella of "energy therapies" and, as with most other energy therapies, the scientific evidence that lends support to its effects is controversial.
This, he adds, is largely due to the fact that colour therapy operates on what is known as "subtle energy" - energy so low in intensity that it is not easily measurable without the most sensitive, up-to-date technology.
As a result, many health care professionals prefer to categorise coloured light therapy as a form of complementary or alternative medicine.
Sylvest says that psychological research mostly supports the short-term effects of colour on human behaviour, but not its long-term effects.
However, William Ludlow, an American architect who in 1921 published a pioneering article called Colour in the Modern Hospital, would argue otherwise.
He stated: "The convalescent needs the therapeutic reaction of the positive colours that nature has spread so lavishly for her children.
"Our eyes were made to find rest and contentment in soft greens, pale blues, an occasional touch of red, but above all, the glorious golden yellow of the sunshine."