Despite colouring that contains no nutritional value, people cannot resist food that comes in vibrant hues. 

It is said that eating a variety of colourful food and vegetables makes for a balanced and nutritional diet. 

And business owners are taking that quite literally, as food and drink are getting a rainbow makeover with edible food colouring. The splash of colours not only gives the dishes a bright pop, but also makes for an Instagram-worthy picture. 

Food colouring is often used in sweet treats, kueh and agar agar. But recently, the trend has crept into savoury items as well, from the coloured xiao long bao (soup dumplings) at restaurant chain Paradise Dynasty to the rainbow cheese toastie from Epicurious cafe at Robertson Quay. 

As Helena Lim, chef-owner of Epicurious, puts it: "We all eat with our eyes, or cameras, first." 

The popular rainbow cheese toastie at the 14-year- old cafe came about when she spotted a picture from street-food stall Grill My Cheese in London on Instagram. It is famous for its grilled cheese sandwiches and, now, its rainbow cheese toast. 

She had planned for the dish to be a Blackboard Special for a few weeks, but it has since been a hot-seller every day. She says: "Rainbow food is happy food. It is impossible not to smile when this plain-looking toast comes on a plain white plate. When you pull it apart, ribbons of colour emerge. The toast is not serious food." 

Another top seller is bottled "Unicorn Tears" from Dapper Coffee in Amoy Street. More than 1,000 bottles were sold over the recent four-day Singapore Coffee Festival. 

Christine Seah, 25, Dapper Coffee’s business leader, is coy about what the glittery blue drink, launched in September last year, contains. 

She says, tongue firmly in cheek: "Our in-house unicorn, Sparkles, was celebrating its third birthday and cried tears of joy when we presented it with a cake and a handwritten card. It was then that we realised these blue, sparkly tears were actually delicious." 

The drink is on sale at Dapper Coffee’s website and the cafe moves up to 50 bottles a day. Those not keen on sparkly "tears" can opt for the cafe’s Gold Brew, which is cold-brew coffee with iridescent dust. 

I Am cafe in North Bridge Road recently launched the rainbow latte. The trend started when a barista in Las Vegas coffee shop Sambalatte added food dye to steamed milk. 

The drink at I Am has been gaining popularity, alongside its rainbow cake and rainbow mille crepe. Up to 450 slices of rainbow cake are sold every week, says cafe founder Muhamad Jamuri, 44. 

Le Halo cafe in Jalan Bukit Ho Swee sells rainbow kueh lapis and rainbow cake. Owner Elia Lim says: "Rainbow food will never go out of fashion as people just love the colours. I used to sell many other types of cakes but, over time, I realised that as long as I have rainbow cakes on display, the other cakes will not sell." 

The food businesses tell The Sunday Times that they use food-grade colouring, in paste or liquid form. 

Peh Hui Yee, a dietitian at the Singapore General Hospital, says: "In general, food colouring contains no nutritional value and does not affect nutrient absorption of food. Nevertheless, they are important components of food products as they make them more appealing." 

She adds that, while uncommon, some people may have allergic or sensitive reactions to food colouring.

"According to the United States Food and Drug Administration, the food colouring tartrazine (synthetic lemon yellow azo dye) causes itchiness and hives in fewer than one in 10,000 people." 

Bibi Chia, principal dietitian of the Raffles Diabetes and Endocrine Centre, says: "There is no recommended amount of food colouring that we can consume. However, we should limit foods that are empty calories. High sugar, vibrantly coloured foods are often marketed at children. We should aim to limit the intake of these foods and choose more wholesome options." 

Yet, diners are so captivated by the vibrant hues that taste is secondary. 

Student Angela Chen, 18, who queued for half an hour at the Geylang Serai Hari Raya Bazaar to buy a rainbow bagel, says: "I’m not really concerned about how it tastes. I just wanted to try it and snap a photo. I wanted to see what the hype is about. It’s on the sweet side, but that’s why I like it." 

Housewife Joanne Lum, 45, who has two daughters aged 15 and 10, says: "I don’t get the fuss over rainbow cakes as it’s mainly food colouring. But it’s the first thing my children will pick when they see it in a cake display, so I won’t spoil their mood. And, the cakes don’t taste bad. Maybe I’ll try to bake my own rainbow cake next time, with natural colouring instead."