Updating the header background color in the Echo theme is quite easy.

Open your /templates/Echo/css/echo.css file:

Find:

/*-----------------------------------------------------------------------------------*/
/*    3.Header (Navigation, Search, etc.)
/*-----------------------------------------------------------------------------------*/
header.pm-top-head {
  display: table;
  position: fixed;
  background: #FFF;
  border-bottom: 1px solid #e8e8e8;

Replace both #FFF and #e8e8e8 with your desired color code.