+2  A: 

You can use the modulus operator to determine if your loop variable ($j) is currently odd or even, and then apply a CSS class as appropriate. In one line, you could change your opening li tag to something like this:

<li class="<? ($j % 2) ? echo "even" : echo "odd"; ?>">

CSS could be applied like this:

.newsfeed li.even{ background: #fff; }
.newsfeed li.odd{ background: #efefef; }

The Modulo Operator for Alternating Rows - Snook.ca

Chris
+1, for a classic, and simple, solution.
David Thomas