Thanks for all the suggestions, folks, I really appreciate it. I am running full RGB, now web colors. In my original posting, both windows were filled with 50% gray. The only difference is that one of window is in RGB mode and the other is in Grayscale mode, as you see from the title bars. Yes, it happens with all shades of grey but not black. In the view menu, I've unchecked the Extras item and the little thingy in the upper right corner of the window disappears, but that's the only difference. I also turned off all extras (actually, none were on). Just to be sure I opened the Show Extras Options dialog (View/Show/Show Extras Options...) and unchecked everything (Selection Edges, Target Path, Annotations, Grid, Guides, Slices) but it makes no difference. I've found that if I choose "View/Proof Setup/Monitor RGB" then grayscale images loose the color cast and look correct, but the color swatch in the tools palette and the thumbnails in other palettes (layers, navigator, etc) still have that greenish cast. So I can work ok, but I just hate mysteries like this! - Bill