When viewed from deep space, like with and reduced to a single pixel or less, Earth appears its distinctive shade for several key reasons, the study explained.

Nitrogen, the overwhelming component of Earth's atmosphere, is transparent. An atmosphere that is clear to visible light preferentially scatters short wavelength, bluer light, as opposed to longer wavelength, redder light. As a result of this so-called Rayleigh scattering, blue light appears to come from all directions, and presto: the sky looks blue, as do the oceans. The blue light as well, and thus to external observers. 

Earth's white clouds boost reflectivity at all wavelengths, diluting the intensity of the Rayleigh scattering. Some red light also mixes into Earth's color palette as it's reflected by the continental land masses. That redness bends Earth's overall color viewed from afar more toward the light blue than, say, the rich azure of Neptune, whose atmosphere's high methane levels absorb red and reflect blue. 

Meanwhile, the oxygen in our air chemically reacts with many types of molecules that would otherwise form an opaque haze. Such atmospheric haze is evident in the visages of Venus, Jupiter, Saturn, and

Earth's free oxygen would not exist were it not for our planet's teeming plant and microbial life, which constantly replenish it through the process of photosynthesis. 

This information in hand, the University of Washington researchers then compiled the spectra of various real and theoretical exoplanets.

"We set about trying to quantify Earth's color and compared it to that of other planets that were not habitable," said Krissansen-Totton.