Sidebar title colors are here. Add this to your CSS edit window (after deleting all the informational text in it).
.sidebar ul li h2, .obar ul li h2 {color: #8DAB3B; }
The two images for the tabs are:
http://s1.wp.com/wp-content/themes/pub/digg3/images/bg_tab_left.gif
http://s1.wp.com/wp-content/themes/pub/digg3/images/bg_tab_right.gif
You will have to make new ones or edit those (keeping exactly the same size) and then upload them to your media library. Get the URLs of those two uploaded files and then replace the URLs in the definitions below (paste the below into the CSS edit window):
#menu ul li a {background: url("images/bg_tab_left.gif") no-repeat scroll left top transparent; }
#menu ul li {background: url("images/bg_tab_right.gif") no-repeat scroll right top transparent; }