Roger Federer settles the 'green or yellow' tennis ball debate

It’s a heated debate which has been disputed online this week as stubbornly as a decisive line call on match point at Wimbledon - are tennis balls green or yellow?

Twitter polls attracting thousands of votes on the surprising issue failed to establish a definitive answer, before Roger Federer finally settled the debate with the same effortless authority he displays on the court.

“They’re yellow, right?” responded the smiling Swiss tennis great to the unusual question from an inquisitive father ahead of the Miami Open.

The colour has been described as fluorescent yellow, chartreuse, lime green and the fun imaginary composite of ‘gellow’, however the official colour for tournament balls is “optic yellow”.

Tennis balls were traditionally black or white, but in 1972 the International Tennis Federation introduced yellow tennis balls after research showed they were more visible to television viewers.

Wimbledon organisers used the traditional white ball for another 14 years until it was switched to the more eye-catching ball for the 1986 tournament.

The tennis ball colour wrangling is reminiscent of the global dress debate which swept social media in 2015 - with some people convinced the outfit was white and gold lace, while others were sure it was black and blue.

Colour expert Andrew Hanson, past chairman of the Colour Group of Great Britain and scientists at the National Physical Laboratory, said at the time it’s all to do with how our brains are wired to see colour.

“We all have memory colours. We know that bananas are yellow for example,” he explained. “Similarly we know that shadow should be blue. It's nothing to do with colour blindness, it's all do to with colour perception. Essentially it is an illusion but people who see white, are actually seeing white, even though it is not really there.”