The research shows that both Uranus and Neptune are closer to greenish blue as opposed to the deep blue hue usually associated with Neptune and the greener shade of Uranus based on images taken from NASA's Voyager 2 mission.

"Although the familiar Voyager 2 images of Uranus were published in a form closer to 'true' color, those of Neptune were, in fact, stretched and enhanced and therefore made artificially too blue," said lead researcher Patrick Irwin of the University of Oxford.

The discrepancy in the colors, long known to astronomers, came about because Voyager 2, the only spacecraft that flew past the two planets, captured images of them in separate colors.

The individually colored images were later put back together in composites that were also enhanced to highlight the planets' details but Irwin said "the distinction became lost over time" when it came to the original colors.

"They did something that I think everyone on Instagram will have done at some time in their life, they tweaked the colors," Prof. Catherine Heymans, Astronomer Royal for Scotland and a professor of astrophysics at the University of Edinburgh told the BBC.

To uncover the true colors, the researchers used data from space-based and ground-based telescopes, including the Hubble Space Telescope's Space Telescope Imaging Spectrograph and the European Southern Observatory Very Large Telescope's Multi Unit Spectroscopic Explorer to observe the planets' colors in more detail.

"Applying our model to the original data, we have been able to reconstitute the most accurate representation yet of the color of both Neptune and Uranus," Irwin said.

The researchers also sought to explain why Uranus' color changes during its 84-year orbit around the sun.

They studied images of Uranus from Arizona's Lowell Observatory dating back to 1950 and found that Uranus takes on a greener color during the summer and winter solstices as its poles point toward the sun, but appears more blue during the equinoxes as the sun aligns with the equator.

Scientists had previously attributed the change to the fact that Uranus practically spins on its side during orbit, placing the north or south pile directly in line with the sun and Earth during the solstices.

The researchers developed a simulated model which led them to believe that a "hood" of methane ice particles that has been observed over the summer pole as it transitions from equinox to solstice increased the reflection of green and red wavelengths at the poles, making the planet appear more green during the solstice.

"In this way, we have demonstrated that Uranus is greener at the solstice due to the polar regions having reduced methane abundance but also an increased thickness of brightly scattered ice particles," Irwin said.

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