How to avoid default background-color in "styles.css"

The "styles.css" for each page automatically contains:

.SCPage {
background-color: #FFFFFF
}

Is there any way to change the colour?
Or a way to avoid that it is automatically added?

I have added in "Page CSS":

.SCPage {
background-color: #000000;
}

The background becomes black alright - but there is an annoying white flash before it gets black.

PS: Is it on purpose that there's a missing semicolon after "background-color: #FFFFFF"?