Over the years, I’ve been accumulating a small database of color spectrums, as part of my C++ graphics library. I’ve been tinkering with a solar-system renderer/simulator lately, and I decided to work on calibrating planetary images. NASA is notoriously bad about punching up the color of planets to make them look more “interesting”.

So what is the average color of the planets? Easily answered with a little digging, because the spectral reflectivity (albedo) has been measured carefully for all of them. Take that, multiply it by the spectrum of the Sun, convert to CIE XYZ, and then convert to 24-bit sRGB, a gamma-corrected color format that computer monitors and HDTV’s are calibrated to display. I scaled XYZ to make Y equal to the total geometric albedo of the planet (but I am not including the effect of distance from the Sun).

I have never seen a correct image of Venus, which is usually an ultraviolet imaged colorized orange or blue or even purple. It fact, to the naked eye, Venus is cream colored and featureless. The Earth is somewhat violet because of the blending of blue with the reddish colored land. And Mars is more brownish-orange than red. Overall, the real palette of the planets is more subtle than usually portrayed.

I added a second set of colors for major moons and the three major asteroid types. Note how dark carbonaceous objects like Phobos and Hygiea are — a very primitive form of matter.

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