Seems to me that all our attempts to portray the "true color" of Mars founder on the lack of a truly objective reference against which to calibrate, and on basic definitions.

Whether it's my frost or Holger's color charts for Viking, or Pathfinder's airbags, what we'd see depends on the color of illumination. Our "white" is terrocentric--we mean "Sol's output filtered through Earth's atmosphere at high noon on a clear day".

Which suggests that we first should define what we mean by white on Mars.

Is it adjusting our sensors so that we see Mars as if it had Earth's atmosphere? This isn't necessarily a bad thing, once we've acknowledged the subjectivity of it anyway. Such an adjustment might make it easier to interpret what we see--e.g., a geologist could more easily identify a mineral if he didn't have to mentally allow for a reddish tinge. To really get speculative, it might also prove beneficial to equip explorers and colonists with color-corrective systems for psychological reasons.

Or should we define white on Mars as what the uncorrected/unaugmented human eye would see (through a clear faceplate), reddish tinge and all?

Well, let me ask a heretical question: Does preserving the reddish tinge in the interest of absolute accuracy really aid in our study of Mars? Is it perhaps useful to calibrate images so that objects are the same color on Mars as they were/would be on Earth, to give our brains a digital crutch?

Enquiring minds, etc......

--Robert