Ahh I see… I kind of thought that may be the case.
Would there be a way to create it using styles on a list element. I can do it with a vertical list, but is it possible to create a horizontal list this way?
You could do this by turning off the native underlining (uncheck the underline links box in the Action) then add the underline back as a CSS border on the bottom of the link. Use padding to generate space away from the text, negative margin in the same amount to bring the text back down to the baseline, and you would have full control over the color and width (and style) of the underline.
The down-side to this is that you would have to figure out the precise CSS selector to use to target those links. If you look in the head of your page, you’ll see a lot of styles that have umpty-zillion asterisks in them. Those are the styles generated by the CSS Menus action. They’re not much fun to read.
Hmm… perhaps its the easier workaround would be to turn off the underline in the CSS palette and then create a graphic space with a gif underline and add it as a background. I guess its cheating but I guess it could work.