What do you mean by “replacement themes for Kubrick”???
For your header go to the style.css and find this:
#header {
background: #5A634E;
background: url(images/header_background.gif) no-repeat;
border: 1px solid #4B5340;
border-width: 0 1px 2px 1px;
color: #fff;
font-size: 18px;
height: 98px;
left: 0;
margin: 0;
padding: 0;
position: absolute;
text-align: left;
top: 0;
width: 768px;
}
and delete the second line:
background: url(images/header_background.gif) no-repeat;
There will be no image.
The other option is: find a picture/image you want, save it as “my_pretty_header.gif” (or .jpg whatever) and upload it in the images folder of the theme AND modifiy the above line in your style sheet accordingly.