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All things bright and edible: Fancy some black garlic, blue potatoes or red cake?

Meg Carter explores the power of culinary colour

How food is presented in a shop or arranged on a plate plays a huge role in how we experience it. If you don't believe that, just watch the next episode of MasterChef. But it's not just when we are fine-dining that we feast with our eyes. The colours we associate with and expect of the food and drink we buy have become a critical commercial consideration for pretty much any product you can imagine – from orange juice and pink salmon, to the purple potatoes and black garlic that are now finding their way into our kitchens.

"Many foods are coloured as a matter of course simply to stand out or meet the specific expectations of consumers that they should look a particular way," says Charles Spence, professor of experimental psychology at Oxford University, who has worked with numerous food and drink companies and with Heston Blumenthal on the commercial and culinary potential of colour. "Blue, for example, is now associated by many younger consumers with the flavour of raspberries," he adds. "Red, meanwhile, is a powerful cue to drive consumer perceptions of sweetness – research has shown you can cut sugar content by as much as 10 per cent but red colour cues can make the consumer think that product is still as sweet."

The colour of food has always been important. It can signify the ripeness of some fruits and the poison contained in others, or the freshness of meat. And colour will naturally vary – by season, or according to exposure to sunlight, temperature or humidity change, and the effects of processing.

Food colour has also long been closely associated with social and cultural factors, including fashion. The origins of the carrot, for example, have been traced back centuries to Iran and Afghanistan where purple, red, white and yellow varieties evolved. The more familiar orange variety became popular in Europe only in the 17th century when it was cultivated as an emblem of the House of Orange and the struggle for Dutch independence.

In recent years, food colour became controversial because of growing concerns about the potential effect artificial food colourings could have on children's behaviour. But while strict regulations exist governing synthetic food dyes, the use and manipulation of colour is widespread in meeting and reshaping consumer expectations.

"There are now so many tricks to ensure things look natural, one could wonder if 'natural' actually exists any more," says Professor Spence. Take that salmon steak you're having for supper later. If it's farmed, the chances are the intensity of its colour has been modified by adjusting the make-up of the food it was fed. Those glacé cherries? Typically, these turn beige during processing, which is why most are dyed red to restore their colour after preserving. As much effort also goes into to ensuring other products, such as yoghurt, are dazzling white.

"Colour is really, really important in food products because customers tell us if something looks colourful, they think it's healthy and nutritious and so good for them – cues we are now working to strengthen across a wide range of our products," says Susi Richards, head of product development at Sainsbury's. The supermarket recently began selling the Purple Majesty purple potato alongside red oranges and yellow raspberries, and it will introduce a candy-striped beetroot later this year.

"It's all about using naturally occurring colours to stand out, nothing artificial," she adds, citing a recent decision to introduce black nanjing rice into own-label mixed salads. "We do add natural colours to some products – strawberry yoghurt, for example – because when we do tastings, it's clear with some foods, especially those white in colour, consumers find it harder to identify the flavour without colour as a cue."

The cues that different colours provide are varied, according to Vicky Bullen, the chief executive of the brand design agency Coley Porter Bell. "Colour can be used to demonstrate natural provenance," she says, "Green, for example, is closely associated with something unprocessed, healthy or organic. Or geographical origin – red and black for Chinese."

Then there are cultural associations. Purple was once a very expensive colour to produce and still signifies premium and indulgence. And bright, bold colours are used in energy-boosting drinks, for example, because there is a consumer desire for the colour of their drink to match their positive mindset.

Bullen is talking mainly from a packaging perspective, but similar principles can be applied to many foods. As well as standing for indulgence, purple has also come to be associated with good health thanks to produce high in antioxidants, such as blueberries. This ia a link that Albert Bartlett, the potato grower behind the Purple Majesty, is capitalising on.

"Purple is a common colour amongst traditional potato varieties – the reason we consider white the norm is simply because they're the ones [Sir Walter] Raleigh chose to bring to Europe," explains Gillian Kynoch, Albert Bartlett's head of development and innovation. The decision to grow purple wasn't just about novelty though. Potatoes are typically seen as a basic commodity. A healthier potato higher in antioxidants, however, is something different.

"As a potato company, we're always looking for interesting things to introduce to persuade people to trade up," Kynoch adds. And the effort appears to be paying off: Purple Majesty's first harvest last autumn attracted a loyal following among middle-aged couples interested in healthier products and culinary novelty.

For the Black Garlic Company, colour provides a direct challenge to consumer expectations – and an attempt to intrigue people into trying the product (which goes on sale in Tesco stores next month). Black garlic is white garlic that's been treated with heat and humidity to age naturally – a three-week process that gives it a shelf life of a year, says Katy Heath, the company's chief executive.

The result is soft and sweet – a flavour reminiscent of molasses and balsamic that's quite different from the taste of garlic home-roasted in the oven. The product can be used either as a cooking ingredient or eaten straight from the bulb as a snack since its preparation eradicates its strong taste and lasting smell.

"People do baulk at the colour, but black food is more familiar now thanks to truffles and the popularity of olives," claims Heath. "In most cases, we've found the novelty of its look persuades people to try it. Though, intriguingly, because we tend to taste with our eyes, some claim at first they think it tastes like liquorice – which it doesn't." Using colour to subvert consumers' expectations has proven a successful tactic for many. Rachel's Organic, for example, used black packaging to create associations with premium qualities – an unprecedented step in the dairy sector, where products tend to be yellow or cream. More recently, Edgerton Distillers has found success with Original Pink Gin which, unlike the cocktail of the same name made famous by Royal Navy sailors in the mid-19th century, actually is pink.

But food companies can go too far. Because colour is often used to help to distinguish between different product variants – semi-skimmed milk is labelled green, while full-fat is blue, and so on – the risk is the consumer ends up being confused. A generation raised on green as a cue for cheese and onion crisps, for example, is still reeling from Walkers' decision to swap this with salt and vinegar's traditional blue.

"Standing out is little good if once the consumer buys a product, it's not what they expect," says Professor Spence. "If what you see doesn't match what you experience, a food or drink just won't make sense and this can significantly limit the chances that you'll buy it again."

Colour decoding the food we eat

Red: to hunter-gatherers, red could denote both ripe fruit and poisonous berries. Today, it's a colour often used to signify sweetness. Recent research has showed that red can be used to manipulate consumers into thinking something's sweeter than it is, thereby masking reduced sugar content.

Yellow: sunshine colours dominate the cereals aisle while drinks companies frequently reformulate orange juice to make it brighter. Uncoloured, margarine resembles lard which is why, back in the 1930s, manufacturers lobbied hard to be allowed to match their product to the colour of butter

Blue: associated with poison during the Victorian era, and is still regarded by some as an appetite-suppressant (have you heard about dieters being encouraged to eat meals off a blue plate?) Today, though, blue is often used to stand out – as with London Gin Company's Original Blue – or to signify low-calorie products.

Green: 'fresh' and 'natural' are the first things many of us will think when we see fresh products that are green. The colour is also widely associated with a diverse array of peppermint-flavoured products – from After Eights to Airwaves and mint tea – as well as eco-friendly and vegetarian food and drinks.

White: traditional associations persist. The lack of colour generally (as well as whiteness specifically) is associated with 'natural' or 'pure'. Yet food companies go to great lengths to ensure the whiteness of certain products meets consumer expectations: the dazzling flesh inside a frozen fish finger is a case in point.

Black: once perceived to denote 'mouldy' or 'rotten', black and darker shades of purple and blue have more recently been used to convey a sense of luxury and indulgence. Meanwhile, the rise and widespread acceptance of the humble black olive is now paving the way for groundbreaking new products such as black garlic.