I finally found a close-up picture of the rover on earth that shows it's TRUE color.  The rover is shown while the rover underwent final checkout March 28, 2003, in the Payload Hazardous Servicing Facility at KSC.

 

http://www-pao.ksc.nasa.gov/kscpao/images/large/03pd3272.jpg

 

Take a good long look at this picture.  What color stands out?  Do you notice that ALL the tied down cable protectors are BLUE?  Do you see any pink ones?

 

Now look at this picture of the sundial that was taken on Mars per it's caption.

http://marsrovers.nasa.gov/gallery/press/spirit/20040108a/PIA05018_br.jpg

 

What color is the cable tie down to the upper right of it colored?  BLUE, just as it should be.  That is why the blue calibration corner on the sundial is blue.  It is the true color.

 

Now look at this picture, which the caption says is color corrected.

 

http://marsrovers.jpl.nasa.gov/gallery/press/spirit/20040108a/color_panorama_sol6-A6R1_med.jpg

 

Forget about the sundial, WHAT COLOR IS THE CABLE TIEDOWN NOW?

PINK!! 

 

This is absolute proof that the colors in this picture are NOT the true natural colors on Mars.  If they were, the cable tiedowns would all be BLUE just as they are in the sundial pictures, which were taken on Mars.

 

It would appear to me that they had the correct color setting for the sundial pictures and changed it on the big picture and either intentionally or forgot to leave out the sundial and cable tie down which would provide the truth.  If you were to change the colors to where the cable tiedowns were blue like they are supposed to be, the color on Mars would be closer to the Canadian version.