This is just a colour issue. You can tweak the colour of that BuddyPress element with some custom CSS…
#buddypress #header-cover-image { background-color: #4a001b }
Go to Appearance > Design Settings > Edit All Default Design Settings and add that CSS to your Custom CSS box
If you use Internet Explorer, Chrome, Firefox, Safari or Opera you can use the browser’s built-in developer tools to point at and “inspect” elements on a web page to find out what styles they use. You can even tweak the styles live to experiment with any changes you might fancy.
References:
http://www.w3schools.com/cssref/pr_background-color.asp