This can be achieved using custom CSS. The header, sidebars, and post are contained within a “.wrap” selector. Setting a background color property on that selector via custom CSS will fill those sections. For example, if you’d like to have a white background, use:
.wrap {background:#fff;}
If you’d like to adjust the left, middle and right columns individually, you may use the “#sidebar”, “#primary” and “#secondary” selectors respectively.
Darken Your Palette

The default color palette for Headline is designed for dark on light tones. If you’d like to switch up your look, and go for light on dark, here’s a good starting point. Remember, all these values are accessible under the Appearance menu, in the Customize sub-section of the Dashboard:
Background color: #1A1A1A
Background Alt color: #222222
Site Title Text color: #EFEFEF
Body Text color: #CCCCCC
Meta Text color: #666666
Sidebar Heading Text color: #999999
Navigation Text color: #666666
Text Shadow color: #111111
Links color: #00CCFF
Borders color: #333333
One final note: be sure to clear the default background image, otherwise your updated background color won’t be displayed!
