ColorTagGen lets you use the MacOS color picker to pick a color. It displays the Red/Green/Blue (RGB) values and the HTML/CSS to be inserted into your web page. It allows you to pick from the 4 possible ways of specifying the color in the CSS Spec.
It also allows you to enter RBG values, or HTML "#FFFFFF" format values and see the color.
The HTML and/or UNIX name of the color is displayed if available, as well as whether the color is Web Safe or not.