Sometimes the skin is rubbed with malt sugar to give it an amber colour and is then hung up to air dry before roasting in the oven.

BBC: Sampling Beijing��s imperial duck

In the three elderly care wards at St Thomas's Hospital doors to toilets and washrooms have been colour-coded with bays to give patients visual prompts in finding their way round.

BBC: Getting it right for dementia patients

The colour of a liquid changes to give either a positive or negative result.

BBC: Cheap colour test picks up HIV

However, the Queen has decided not to give permission for a change of colour for her official London residence.

BBC: Queen answers Irish bid to turn Buckingham Palace green