I often find the need for a color picker, so I wrote an application for one. It uses the java JColorChooser widget to set foreground and background colors and informs the user of the decimal and hexidecimal equivalents.
This jar file is an executable. In windows, where you have Java installed, download the file, then just click on it with the mouse to run it. Or to run it in place, right click and choose to open the file where it is.