Mars’s colour
Why is Mars red?
The dust is rust. Iron in Martian rock has oxidised, and that red-brown powder is blown across the whole planet, so even the sky looks butterscotch. The rocks underneath can be darker; the colour you see from Earth is a planet wearing its rust. Open Mars and its moons to look at the globe.
Rust, then wind
Early Mars had water and a thicker air. Iron in the rock rusted — the same chemistry that turns a bicycle orange, just much slower and across a whole world. When the water went, the rust stayed as dust.
Mars’s air is thin, but it is enough to lift that dust. Storms can wrap the planet. What you see through a telescope is not bare rock. It is a coat of iron oxide, grain by grain.
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Not every rock is red
Rovers have found grey-blue rock under the dust, and dark volcanic plains that only look red when the powder sits on them. The colour is a surface story. The planet underneath is a mix, like Earth, just drier and rustier on top.