the only reference to this problem that I could find was:
There it is noted as a CS3 Problem and not addressed further.
However, it gave me quite a hard time and looks like follows:
That is, when I use the color picker (left circle) - no matter if that of the "Fast Color Corrector" or the "Three Way Color Corrector" - and hover over the program monitor (right circle) the colors do not match at all. Observing the active color sample while hovering the mouse pointer over any part of the screen reveals no correlaction whatsoever.
I double checked with Photoshop CS5, Illustrator CS5, After Effects CS5 and Premiere Pro CS4. They all work correctly.
I then checked on another system and got a surprise: There it worked.
I then filtered the problem down to the following: Both systems have two monitors. However, the system where it works correctly is a MacPro with two identical monitors (1920x1200). The system on which it does not work is a MacBook Pro with a native 1440x900 screen and an Apple LED Monitor (1920x1200) attached via Mini Display Port.
Both run Snow Leopard (10.6). The MacBook Pro has a NVIDIA GeForce 9400M while the MacPro has a ATI Radeon HD 4870.
There is a limited workaroud: When I plugged off the secondary monitor (LED) to be left with a single display (native notebook monitor) then the color picker works correctly.
It also works correctly, when I deactivate the native monitor and only work the the attached LED display.
Finally, I think I got it narrowed down: On the laptop I set both monitors to an identical resolution, 1200x800 was the greatest common factor, and first it did not work. Then I realized that there was still the "monitor arragement" adjustment (System Preferences -> Displays). So I arranged both monitors symmetricaly side to side. And voila: the color picker worked. For a final double check, I returned to the dual screen MacPro system where it worked from the beginning. I brought the "monitor arrangement" out of symmetry and again voila: The color picker did not work anymore.
Well, on the laptop the problem remains since both monitors are not of identical resolution. So the only viable option there is to work on a single monitor.
But maybe this description gives the people at Adobe enough hints to tackle the issue?