If you use transparencies on your map, you may get frustrated trying to match up your legend with map colours. Pixie is a small application from Nattyware that will tell you the colour of any pixel on your screen in either RGB, CMYK or HSV. You can download it from here: http://www.nattyware.com/pixie.html

(Hint: if you turn on Caps Lock, Screen Lock and Number Lock all at once, you can freeze the colour in the application window.)