-2
Assume you want the second tab to have a different background, you can try adding the following lines to the mctabs.css file:
ul.mctabs li:nth-child(2) a {background:black;}
ul.mctabs li:nth-child(2).selected a {background:green;}
You also need to check other li a selectors such as ul.mctabs li a:hover and insert nth-child(2) into it.
Above is not supported by IE 8 and earlier.
I've only tested them in Chrome. It seems
ul.mctabs li:nth-child(2).selected a {background:green;}
can also be written as:
ul.mctabs li.selected:nth-child(2) a {background:green;}
But I haven't tested it in other browsers.