Support?

Ok so im new to CSS and was wondering if anyone can help me find the section of the CSS file where i can change the white background,

I have tried to edit this line

body, html {
    background: #FFF url(site-img/body_bkg_default.png) repeat-x;
    font-family: Helvetica, Arial, sans-serif;
    padding: 0; margin: 0;
    color: #FFF;
    }

but it did not work for me, but this is the color i am trying to make the background, #a4a4a4
i am also wondering, most of the color codes are 3 digits not 6 ??

Any help would be great.

Thankyou