Anybody who's messed with the OS X color chooser has noticed that it's quite a versatile tool with lots of nice features. However, there's one glaring
deficiency that rears its head if you try to use it in conjunction with web
design. Say you've picked a nice palette for your website using the color
picker and want to code it up. All you need is the hex values of your colors.
Uh oh. The color picker has no way to show you the hex values of your colors!
Astonishing, but true.

Luckily, Lucky Software has written a plugin for the color picker (who knew that
there were such things??) that provides this functionality. It can display the
numerical representation of your colors in a variety of formats, including
#rrggbb, #rgb, rgb(%r, %g, %b), and rgb(rrr,ggg,bbb). It will also tell you if
a color is “web safe.” I think the only thing conceivably missing in this
little plugin is the ability to display values in HSV and CMYK color spaces,
but that's understandable since it was designed for the web, where RGB is king.

You can get HexColorPicker at http://www.luckysoftware.dk/hexcolorpicker.php

Another interesting color picker plugin can be found here.