It sounds like it was out of alignment.  If it is rotated wrong then it
will make things look worst not better.

Scott

Hi
Similar problems with C.Pol filter when used with lens which rotates to zoom
& focus - track a moving object and continuous shoot and you can see the
difference in shades of cast. As far as I know it is not a problem with
lenses which have internal movements to focus and zoom.  The final element
of the lens must not rotate if you are to use the filter in moving shots or
where you don't reset after / before every shot.  ......  I may stand
corrected on that, certainly be good to have an experts view point.
Good luck
Hew

I sometimes have trouble determining when the polarizer is aligned
correctly and noticed that there is a color shift in some circumstances,
I'm not even sure whether max effect is indicated by the warmer or
cooler phase but there is a change in color cast (sometimes). Try a shot
at 90 degrees to the sun to confirm this problem under those conditions.

Are you shooting with a preset WB? Auto WB should correct for this.

Also possible that it's picking up pollution in the air more clearly??

Here's something interesting:
http://dpfwiw.com/polarizer.htm#fun
"Fun with a Reversed Circular Polarizer—An Instructive Diversion

Look at a polarized light source through your CP with the male threads
pointing away from you, and you'll see some very interesting color
shifts that nicely illustrate several important polarization concepts,
thanks to the surprisingly complex optical properties of a typical QWP.
Henceforth I'll refer to a CP held male threads away as a reversed CP.

    Marks the paydirt In a nutshell, a reversed CP acts like a ~2-stop
(75%) neutral density filter with an adjustable warming or cooling
effect, depending on its orientation. Maximum bluing comes with the
polarizer turned to block the incoming polarized light. Maximum
reddening occurs at 90° to the bluest setting and neutrality at any 45°
setting in between."

Auto white balance should be turned off...the polarizer can trick it.  
So set the balance to something...also make sure the latest firmware is
in the D70, I think there was an issue with white balance settings on
it.....

JR