Astronomers at the Mauna Loa Observatory in Hawaii discovered that blue light reflected from Earth turns turquoise when it bounces off the Moon.
"This is the first accurate colour measurement of the dark side of the Moon," said Peter Thejll, a senior scientist at the Danish Meteorological Institute in Copenhagen and first author on the study.
Researchers installed a telescope and a sensitive camera at the observatory to take measurements of the Moon for two years.
The dark side of the Moon is not the same as the far side, which gets as much sunlight as the side facing us. The dark side is not lit directly by sunlight, but by light reflected from Earth, 'The Guardian' reported.
"This is sunshine that struck the Earth, was coloured by the Earth, was reflected up to the Moon, struck the Moon, and then came back to us," Thejll said.
Images of our planet from space show that the planet looks blue. But when this blue light strikes the Moon, the light that's reflected back is turquoise.
"Astronauts standing on the Moon and looking up at the Earth described it as a blue marble," said Thejll.
"Having not been into space myself, I don't know what they meant exactly, but once that blue light strikes the Moon's surface, it shifts to a blue-green colour. We can call it turquoise," he said.
To measure the colour of the dark side of the Moon, the researchers first screened out light from the bright side that had been scattered by Earth's atmosphere.
This scattered light produces a shifting halo around the Moon and disturbs measurements of the dark side.
Astronomers snapped pictures of the Moon through the telescope using two different colour filters. Amid hundreds of images, they found a pair taken of the waning crescent Moon on 18 January 2012 that had exactly the same halo.
When they subtracted one image from the other, the halo disappeared and they could measure the true colour of the Moon's dark side.
Thejll said that observations of the dark side of the Moon can help scientists to monitor the colour of the Earth, which could be useful for assessing climate change models.