Here is a cute little program called Pixie that gives the exact color codes for any color on the screen that you can point to with the cursor (mouse). This is an old Windows program I have had for several years. It is really handy when you need to match colors exactly for web page development or other design tasks.
Even though it is a Windows program, there is no install needed. Just run the .EXE program. Here is a screen shot of Pixie telling me the color code of the green in the Mint 12 logo on the standard desktop.
The Pixie.EXE download is available from this page: