WOW thanks. I actually asked this cause I haven't used my 70-200 too much lately, but on the last occasions it did see action, my images came out with a very gray cast. Like fog. Usually it was easily corrected with auto-levels, or one some occasions, manually setting the levels for best results. it happens on my 50mm prime too, but not nearly to the same extent. The results still get very good after I correct levels, but sure, I loose information and gain some grain on the process, and that's unwanted stuff..
I've always used AdobeRGB in the camera, but can never remember my zoom giving so bad results as I've seen lately (as said, quite a time since I used it now). But when thinking back, I've ditched Photoshop in favor of Gimp since the last time I did any serious action with the 70-200 zoom. And Gimp doesn't complain, when opening AdobeRGB, but neither does it have an option for changing colour-modes (only between rgb, grayscale, index). I think I fire up photoshop and see if the images turn out the same, or there are a difference. Cause either my camera or zoom-lens have run into some serious trouble now (hopefully not), or I have to revert it back to sRGB, even though I loose some info, I definetly don't loose as much as this "gray-haze" problem is causing me..