I tried using colormatch and is showed the same issue as ProphotoRGB. Pursuing the Gama idea, I found under the GPU settings a section in the advanced control labled "Debug" within this there is an option to select "Gamma Corrected".
This seems to have solved the color display issue, but now I am not able to smoothly drag a window. When a window is moved, the window frame does not fully redraw.
It looks like there are some issues to be worked out between the nVidia driver (my current version is 182.50) and CS4.
thanks for all the ideas.
I think Damo's on the right track with the gamma issue.
Sounds like you get a different gamma when Photoshop CS4 uses the GPU for on-screen manipulations, but not the right one when rendering without the GPU.
I don't know what lies in the Preferences | Performance | GPU settings area; does the Advanced button give you any sort of gamma control?
Step one might be to get the GPU rendering and the regular rendering to agree (even if both are dark), and then to hunt for the root cause (video card settings, look-up-tables, etc., for example) that would fix both.
Sorry I can't be of more help, (my video card is too old and CS4 doesn't recognize it as suitable for acceleration.)