My Tiffen Graduated Neutral Density- Problem with my Olympus E1

When I use this fairly expensive graduated neutral density filter to prevent
overexposure
of the sky for landscapes, sometimes the sky color gets messed up turns
a little (or a lot) purple. I've tried lots of different things but can't
make it work. Do you
think it is an issue with the CCD? Can you think of a way to make it work,
or have
you tried the same combination yourself?

Please see URL for example with and without the filter for comparison

thanks


Larry

http://freycard.com/4shots.jpg