>with a camera we get rendering of numerical values of colour, rather than subjective impressions, and when you view those onscreen sometimes they look odd indeed.

could you elaborate please Nick? it seems a subtle but significant point.
.. isn't a camera basically a mechanical version of the eye's lens & retina? So, as long as the lander's colours match the known/expected ones, then the rest of the scene should be 'true'. Subjective impressions would then be the next stage in the chain, I thought..
Don Davis (http://www.donaldedavis.com/PARTS/MARSCLRS.html) does explain the issues well but i thought that proper ground-lander colour calibration would manage those problems. OTOH there are apparently brightness and scattering issues too, which would be hard to determine from here. A good calibration with a colour chart on a lander (ie. close-up) would then maybe not guarantee accuracy in medium and long-range images

Daniel