It's a quandary which has left philosophers scratching their heads for centuries: do we perceive colours in the same way, or is one man's yellow really another's green?
Last year's #thedress phenomenon, which divided the world as they tried to figure out whether a dress in a photograph was blue and black or white and gold, suggested people's perceptions may be different.
But now a new study has given another insight into the eyes of the nation: is this colour blue or green?
Optical Express reckons 64 per cent of Britons think it's more green, while 32 per cent reckon it's blue.
That said, once the colour is put next to others, the company said many people changed their minds - with 90 per cent deciding it was actually green.
“Light enters the eye and hits the retina, which is the light sensitive tissue at the back of the eye," said Stephen Hannan, clinical services director at Optical Express.
"The light is converted to an electrical signal which travels along the optic nerve to the visual cortex in the brain. The brain makes its own unique interpretation of this electrical signal.
“It is not surprising that many respondents changed their mind when seeing the colour in contrast to the two blue shades, as we perceive an object’s colour based on a comparison to its surrounding shades, not on the actual colour itself.”
Forget the EU referendum - this is the real question dividing the nation...