Here is the simple tip to change the header backgound color in Blogspot.
By assinging some color code to background-color style in #header in Template Css,we can easily change the header color
#header {
margin: 5px;
border: 1px solid $bordercolor;
text-align: center;
color:$pagetitlecolor;
background-color:#5588AA;
}
For the detailed post visit here
http://www.bloggertipsandtricks.com/2009/04/baby-customization-step-header.html