[techhead]

if your out to change colour, all you need to do is edit the style sheet:
skin1/skin1.css

the styles to look out for are:
DialogTitle ... (the title bar)
DialogBorder ... (the border arround the box)
DialogBox ... (where the content goes)

I always edit the skin1/dialog.tpl file and remove the following bit of code:
background="{$ImagesDir}/dialog_bg_n.gif"

only because I think the image used in the dialog title is butt ugly, if you do this you will want to change the DialogTitle font colour to something other than white.

good hunting!