If you're using respone.menu to build your menu and in line with http://www.web2py.com/book/default/search?search=response.menu you could replace the second item (the boolean value)in the tuple with the check (request.function=='index') where index is your active page. In this way web2py automatically add to li tag (your menu tab) the class="web2py-menu-active". So in .css file you can customize it.
For example (I'm using default w2p application "welcome"): ### in menu.py (welcome app models folder) ### response.menu = [ (T('Home'), False, URL('default','index'), []) ] becomes response.menu = [ (T('Home'), (request.function=='index'), URL('default','index'), []) ] ### in layout.html (welcome app views folder ### change this {{=MENU(response.menu,_class='sf-menu')}} to {{=MENU(response.menu,_class='sf-menu',li_active="tab_highlighted")}} li_active allows to change default class "web2py-menu-active" to your preference. In the above example "tab_highlighted". ### in base.css (welcome app static/css subfolder) append the css rule .web2py-menu-active a, .tab_highlighted a{color:red} Ciao. Paolo