B+W 77mm 110 color cast

[Haiyan]

I used the B+W 77mm 110 (10 stop) filter on my Nikon D90 and 10-24mm lens. the exposure was about 25 sec. and color of the image seems less saturated to me and there seems a layer of dark fog on it.

There isn't supposed to be a color cast on NG filters. but every shot I took with this filter and this camera set, seems to have lost its color saturation.

Any suggestion on the reasons and how to improve it?