Gpick

Gpick is an advanced color picker and palette editing tool. It has a magnifier, precise mouse pointer control using keyboard, etc.

You can export color data to various formats including Inkscape/Gimp Palette (*.gpl), Adobe Swatch Exchange (*.ase), Alias/WaveFront Material (*.mtl), and Cascaded Style Sheet (*.css).
Windows version of Gpick requires GTK libraries to be installed, or it will not run and complain about missing dll files.