"Use custom background color for web pages" override web site author's stylesheet.

[whileloop]

I think the option "Use custom background color for web pages" should only override the user agent's default background color (white), but not override web site author's stylesheet.

If I really want to overwrite background color style of web pages, I can add style rule to "User Data/custom.css"
body {
    background-color: lightgray !important;
}