You're using a Template Monster template that has completely re-written the template structure, invalidating most if not all of the normal Zen Cart styling solutions that you'll find on this site. Indeed, it seems odd that they have included the Zen Cart CSSat all, since it doesn't appear to do anything other than cause confusion and slow your site down.

To do what you say you want to do, you would need to find the following block in your stylesheet_tm.css
.user_menu2 li a {
color:#000000;
display:block;
padding:2px 31px 3px 45px;
text-decoration:none;
}
and change it to
.user_menu2 li a {
color:#999966;
display:block;
padding:2px 31px 3px 45px;
text-decoration:none;
}
Though I suspect that you will find that the links are virtually unreadable on the green background.