Is there a ‘map’ which describes what each section is called?

This is only a guess but I think that space is all part of the background. (a guess because no link to your site or a theme demo).

body {
background: #ffffff;
color: #222222;
font-size: 12px;
font-family: Arial, Tahoma, Verdana;
margin: 0px auto 0px;
padding: 0px;
}

Find that in the style sheet (if I even have the right theme) and change #ffffff to #000 and you will see what I mean.

You could do this: (again, if I have the right theme);

body {
background: #000;
color: #222222;
font-size: 12px;
font-family: Arial, Tahoma, Verdana;
margin: 0px auto 0px;
padding: 0px;
}

#wrap {
background: #FFF;
width: 940px;
margin: 0px auto 0px;
padding: 0px 20px 0px 20px;
}

…and then tweak it from there using whatever colors you want and then fixing the little visual things that will pop up due to the alterations.

Thank you, Clayton!

I’m glad it helped!

You can also use: background-color: #000;