You can also edit the template.css file and replace the background image references with a CSS background color reference instead of modifying the files, if you're not handy with Photoshop... just figured this out myself somewhat accidentally.
body {
color:#191919;
background:url(../images/s5_bg.jpg); <--- replace this line with " background-color:#FFFFFF; " to make it white
font-size:0.8em;
line-height:140%;}
#s5_header_area1 {
background:url(../images/s5_bg_top.jpg) no-repeat bottom center; <--- ditto
height:200px;
margin-bottom:-30px;
}
#s5_footer_area1 {
background:url(../images/s5_bg_bottom.jpg) no-repeat top center; <--- ditto
}