Why Mars looks red
Claim in the list: Mars’ red hue is caused by oxidation of iron in the soil.
Verification: Confirmed in broad terms. Iron minerals in Martian rocks, regolith, and dust are oxidized; reddish iron oxides give the surface its characteristic color. Research continues to refine which minerals and processes are responsible: NASA has reported that water-bearing ferrihydrite may be an important component of the red dust. Mars is not uniformly coated in “rust,” and surface colors vary with local geology and dust.
Conclusion: Oxidized iron in rocks and dust is the main reason Mars looks red; “iron in the soil” is a reasonable simplification.