the fix for all things formatting - colors, backgrounds, fonts, etc - is in style.css of your theme:
(this involves learning the basics of css)
this is for the header:
#topnavbar {
background: #93BBBC url(images/topnav.png);
width: 960px;
height: 30px;
color: #FFFFFF;
margin: 0px;
padding: 0px;
}
for sidebar:
#sidebar h4 {
background: #86AFB0 url(images/headline.png);
color: #FFFFFF;
font-size: 11px;
font-family: Arial, Tahoma, Verdana;
font-weight: bold;
text-transform: uppercase;
margin: 0px 0px 10px 0px;
padding: 3px 0px 3px 7px;
}
for categories:
#content h3 {
background: #86AFB0 url(images/headline.png);
color: #FFFFFF;
font-size: 11px;
font-family: Arial, Tahoma, Verdana;
font-weight: bold;
text-transform: uppercase;
margin: 0px 0px 10px 0px;
padding: 3px 0px 3px 7px;
}
these also have background images which you may need to edit.
(in the /images folder of the theme)