You might think you know what colour a tennis ball is, but it seems at least half the population disagrees with you.
A recent poll shows that there is a near-even split between people who think the balls are green and those who think they're yellow.
Almost 30,000 people responded to a Twitter poll on the issue, created by someone trying to "resolve a marital dispute".
Fify-two percent of respondents believe tennis balls are green, 42 percent say yellow, and an undecided 6 percent opted for "other".
The Project host Jesse Mulligan said tennis balls are definitely yellow, while Kanoa Lloyd is certain that they are green.
Guest host Jacquie Brown opted for a third option, saying that tennis balls are "a greeny yellowy green".
The Wimbledon Tennis club website says that the colour of its tennis balls is actually called 'optical yellow'.
The Project team conducted an experiment with a green screen, in an attempt to determine the colour.
Watch the video above.