A UK-based psychologist explained the reason behind the red-and-yellow logo of popular fast food chain McDonald's.

Karen Haller, an expert in behavioural colour and design psychology, said the iconic Golden Arches design was created to elicit specific psychological effects on customers.

In a blog post, the design consultant said: 'Looking at the positive psychology qualities of red and yellow in relation to the fast food industry, red triggers stimulation, appetite, hunger, it attracts attention. Yellow triggers the feelings of happiness and friendliness.

'When you combine red and yellow it's about speed, quickness. In, eat and out again.'

The red and yellow palette noticeably dominates any McDonald's branch - from the mascot Ronald McDonald usually inviting customers outside, to the colour of the store counters, and even the french fry containers.

The colour scheme is also used by other famous fast food brans like KFC, Burger King, Wendy's, and Pizza Hut.

Karen, who runs a behavioural design firm, added: 'The language of colour is communicated quicker to the brain than words or shapes as they work directly on our feelings and emotions.'

McDonald's was founded in 1940 in Downey, California, and has since spawned into the world's most recognisable fast-food outlet. In recent years, the brand has incorporated green and black to create a healthier image.

Karen says the company wanted some of its restaurants to appear more inviting than a quick stopover.

She added: ‘Green elicits the feelings of nature, natural and environmentally friendly. It's no longer about rushing in for a quick bite to eat.'