This might be useful: http://samples.msdn.microsoft.com/workshop/samples/author/dhtml/colors/ColorTable.htm

What you you mean "HEX to RGB" and vice-versa? RGB is given in HEX values (3 or 6 digits).

Add: look around for other color name to RGB (HEX) files. I think there's one that comes with XWindows that's got more colors than the link I gave above. Regarding HEX/RGB, were you were talking about decimal triplets (0, 0, 255 instead of 'blue' or #0000FF)? That's a simple mechanical reformatting in either direction. Triplets are still used in some primitive systems, but 6 hex digits are used in HTML and CSS.

http://web.njit.edu/~kevin/rgb.txt.html
http://support.esosoft.net/counter/rgb.html
http://en.wikipedia.org/wiki/X11_color_names
http://people.csail.mit.edu/jaffer/Color/Dictionaries