you will need to add some new css code
You can change the "selected" color in the stylevar. For hover color go to template
additional.css
Add the following, feel free to customize the color
Code:
.navtabs li a.navtab:hover {
color:#ffffff; /* Color of text for hover */
background-color:#000000; /* Color for background of button when hovered */
}
Now if you'd like to use an image for the background button hover then use
background:url(hxxp://urltoimage.png) #000000 no-repeat;
as opposed to background-color