You could have clients create a color profile before they select a sample and then adjust swatches accordingly. There are methods for doing this (albeit complex) so here is the only site I have bookmarked that has such a solution. The tool is their monitor calibration tool.
http://easyrgb.com/index.html
Color on the web is a tough subject. I really have a hard time matching since I have such bright lcd's. Good luck.
-Jim