Gwent Police have abandoned the greys, browns and beiges of the 20th-century police cell and have used colour psychology to decorate them.

Ystrad Mynach station, which recently opened at a cost of £5 million, has four cells with glass doors for prisoners who suffer from claustrophobia. Designers have painted the frames yellow, which researchers say is a calming colour. Other cells contain a royal blue line because psychologists believe that the colour is likely to encourage truthfulness.

The station has 31 cells, including 12 with a “live scan” system for drunken or disturbed prisoners, in which transmitters detect the rise and fall of their chest. An alarm alerts officers if a prisoner’s breathing stops and carries on ringing until the door is opened.

Designers and psychologists have worked for years on the properties of colour. Blue is said to suggest trust, efficiency, serenity, duty, logic, coolness, reflection and calm. It also suggests coldness, aloofness and unfriendliness. It is thought that strong blues will stimulate clear thought and lighter, soft shades will calm the mind and aid concentration.

Yellow is linked with optimism, confidence, self-esteem and friendliness. Get the shade wrong and it could provoke irrationality, fear, depression and anxiety, but the right yellow can lift spirits and self-esteem.

Ingrid Collins, a psychologist who specialises in the effects of colour, said that colour was an “energy force”. She said: “Blue does enhance communication but I am not sure it would enhance truthful communication.”

Yellow, she said, affected the mind. Red, on the other hand, should never be considered because it could increase aggression. Mrs Collins praised the designers for using colours in the cells. Gwent is not the first British force to experiment with colour to pacify or persuade prisoners to co-operate. In the 1990s Strathclyde Police used pink in cells based on research carried out by the US Navy.

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