Peacock Color Picker is a free application for Windows that lets you select any color that appears on your screen in a way that's quick and reliable. You'll also get extra functions that aren't offered by other color pickers.
The method that this tool uses includes taking a screen shot of a particular area of the screen so that you can later use it to select the desired color from the program's interface.
It also provides other capture methods, like opening up an image from your hard drive, generating a random color, or using pre-chosen color palettes or ones that you've already saved. All of this makes Peacock Color Picker a great tool.