What colour is Mercury?
The colour of the planet Mercury
Short answer: Gray.
Long answer: The surface of Mercury is made of rocky material. Although there are craters and mountains, there is essentially no atmosphere and no geological activity, so there's nothing to change its appearance. All we see from space is the rocky surface, which is various shades of gray.
It is possible that there could be occasional volcanic activity which could provide some variation in colour, but not enough to change the overall colour of the planet.
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