Step 1.
Select the eye dropper.

Step 2.
CLICK in your document and HOLD the mouse button down
Step 3.
Drag eyedropper outside and PRESTO... its now sampling colors outside the program.

Release when you have the color you want.
If you play with the sample size option in the eye dropper, it might help you select colors accurately. Especially if its some what pixelated.
This is captain WOWZERS signing off..
*CLICK