Toggle Transparent Menù

Hi, here's Jacopo, i need a small help for avoiding the transparent menù in the pages (an example here: http://www.andreacapezzuoliecompagnia.it/calendar/ ). My problem is that i need the menù "section" not to be fully transparent when starting a page, i need it "transparent-black" like when scrolling down... Thanks in advance for any help! Regards Jacopo