You can still use the WPF one which you could host as a control within a windows form. The WPF/Winforms integration is pretty cool : You can read more about it over here (at my blog actually) : http://sachabarbs.wordpress.com/2008/02/26/winforms-wpf-interop/
You may need to jiggle the WPF color picker a little to expose a property for color which is accessable from the hosting winforms form, which you would show as a dialog