Here's the 1.0 version of a small WPF prorgam I made that makes gathering screen colours, comparing them and editing them a breeze so that it is really easy to get the hex for the colour you are after. You can then copy the appropriate representation (ARGB, RGB, HSV, CMYK) of the colour to your clipboard to copy direcly into the XAML code.

The sorting is pretty dodgy - after all sorting colours in 2D is a nightmare!

Anyway here's some screen dumps, feel free to use it however you want, any updates I'll add to this blog, although it is unlikely there will be many.

Anyway OS requirements are:
Windows XP SP3/Vista/7