Actually, the biggest problem (that I've seen) is the fact that the blue patch on the MarsDial happens to be particularly bright in the near-infrared range. Since nothing that Mars Express is imaging has that strange property (that is, is much brighter in near-infrared than in red), no one notices Mars Express's color differences.

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"Nobody understands quantum physics." -- Richard Feynman

"So, does quantum physics predict circular orbits for electrons?" -- Student in my Intro to Quantum class

Showing that Feynman was especially correct about some individuals.