Question

Don't assume my background color is white.

Can we change the default CSS so the background colour for the body element is specified explicitly.

Answer 1

You can change the background color through Admin > Themes > Custom CSS to any color you like.

Answer 2

Agreed, Stack Overflow et al have the background colour set. The default stylesheet should do the same.

body{background:#fff;color:#000;...

Currently the CSS for SE sites is as follows:

html, body, div, span, applet, object, iframe, h1, h2, h3, h4, h5, h6, p, blockquote, pre, a, abbr, acronym, address, big, cite, code, del, dfn, em, font, img, ins, kbd, q, s, samp, small, strike, strong, sub, sup, tt, var, b, u, i, center, dl, dt, dd, ol, ul, li, fieldset, form, label, legend, table, caption, tbody, tfoot, thead, tr, th, td
{
	margin: 0;
	padding: 0;
	border: 0;
	font-size: 100%;
	vertical-align: baseline;
	background: transparent;
}

Answer 3

I see this rule in the default stylesheet:

/* Default styles */
body {
    background: #ffffff;
    color: #555555;
}

Is this not showing up in your CSS?