In page options you have light or dark backgrounds. To change to different colors just open /js/scripts.js and at line 388 you will find

if ($("#page-content").hasClass("light-content")) {
$("main, nav").css('background-color', '#0f1010');
$('#magic-cursor').addClass('light-content');
if( $('#hero').length > 0 ){
if( $('#hero').hasClass("has-image")) {
$("header").css('background-color', 'transparent');
} else {
$("header").css('background-color', '#0f1010');
}
}
} else {
$("main").css('background-color', '#fff');
$("nav").css('background-color', '#0f1010');
$('#magic-cursor').removeClass('light-content');
if( $('#hero').hasClass("has-image")) {
$("header").css('background-color', 'transparent');
} else {
$("header").css('background-color', '#fff');
}
}

$("main").css('background-color', '#fff'); 

or depending on the setting

$("main").css('background-color', '#0f1010');

is actually what sets the page background color