Re: How to edit this part of the default template?
The different shades of gray are rendered by background images for certain pages of the theme. It’s been some time since I created a child theme for bp-sn-parent, but these selectors should get you started:
background: #ffffff none;
where you can change #ffffff to whatever color you want and “none” in effect says no background image for these pages.
You add that style at the bottom of screen.css located in BP 1.1.3 bp-default/_inc/css/ folder.
Or to be BP-correct, uncomment the following
@import url( _inc/css/custom.css );
in your bp-default style.css and create custom.css file in bp-default/_inc/css/ folder and add above style to custom.css.