The American dollar, rather like Mr Ford’s motor car, comes in any colour – so long as it’s green.

Given the American taste for multicoloured flamboyance and limitless variety, it looks odd to British eyes that all denominations of the stuff that makes the world go round are only available in the one colour.

In most countries, including Britain, banknotes come in an assortment of shades and sizes. The £5 note, having gone through incarnations of white, then blue, is currently green and blue. A £10 note is brown and a twenty is purple.

Neither British nor American currency sparkles, but both have their origin in glittering metals with an alluring heft and shine – and some people in the US think that time should come again: they want to return to gold. It’s no accident that British currency, the pound sterling, has the same name as a unit of weight. It was originally worth its weight, not in gold, but silver.

The US dollar started life as a silver coin, inspired by the Spanish dollar – better known as the ‘piece of eight’ beloved by pirates. ‘Dollar’ is a variation on ‘Thaller’, a German coin named after a valley in central Europe where silver was mined. Gold replaced silver as the bankers’ metal of choice in the 19th century. The gold standard meant that, in theory, you handed over your banknote and you received a chunk of the precious metal in return.

On British banknotes, it is explicit that the piece of paper is merely a symbol. Written on each note is the declaration: “I promise to pay the bearer on demand the sum of…”. The dollar merely says: “In God we trust”, prompting some to observe that American consumers don’t have quite the same faith in bankers.

Britain left the gold standard for good in 1931, but the US held fast until 1971 and there’s now a significant political movement in the US to return to gold. To supporters, what looks like a big problem is seen as part of their case: all the gold mined in the entire world since the beginning of history isn’t quite enough to back up the amount of money in circulation in the US at the moment.

Critics say reverting to the gold standard would mean chaos. Fans say it would stop governments – and everybody else – borrowing too much. 

From BBC Knowledge Magazine issue 19

British BBC journalist Mark Mardell lives in Maryland and is the BBC’s North America Editor. Read his blogs at www.bbc.co.uk/blogs/thereporters/markmardell and follow @MarkMardell