Like the infamous dress some people thought was blue while others swore was white, Roger Federer has sparked a great debate over the colour of tennis balls.
Like some, you're probably thinking "Isn't it obviously that they're yellow?"
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Fluorescent yellow to be more precise.
Well that's what Federer thinks too but he didn't sound absolutely convinced when asked by fans in the video at the top of the page.
The clip posted on Twitter has been viewed more than 380,000 times (at time of writing) since it was uploaded.
No doubt to the surprise of the Swiss maestro - it's set off a whole raft of arguments all over the world with some adamant yellow is the answer, while others vehemently argue it's green.
Are tennis balls really yellow or are they green?
A key argument in the Yellow corner would surely be that if Wimbledon is played on green grass then surely the balls they use can't be green as well.
Thankfully, in order to settle this great debate, fans have been quick to provide us with a scientific explanation that the colour in fact lies halfway between both yellow and green.
Admittedly, much like the blue dress (you know it was) - it's doubtful whether this will do much to quell those heated debates you're now surely having with friends, family and work mates.
Nether yellow or green its chartreuse. pic.twitter.com/sT2kM4UxLz— Jamie Davies (@MRM4N1) March 21, 2018