How to extract the true color of Mars
What is that?
Same color scheme on Viking 1 pictures from '76
The Pathfinder Lander
Another Pentagonal Pyramid on Mars!
  page 4 of 12

In 1976 Viking 1 and 2 also took some very good pictures.
The same color scheme was used 20 years ago:

Original NASA Picture
from Viking 1

Image created by me from the 3 RGB filtered frames with the described color correction (ID 11H016)

Snow on Viking 2 landing site. (ID 21I093)
Here we could make a perfect
White Calibration,
but do not need to, as the original
image data is already OK.

Read more about Snow and Liquid Water
in this report from Levin & Levin

A picture from Bild der Wissenschaft (02.1977) shows the first Viking 1 color-picture
which was later "color corrected" without any scientific reason.

All images from Viking courtesy of JPL/NASA/Caltech.

Holger Isenberg