<?php // PHP version
  $i = 0;
  // have_rows_to_output is a stand-in for your loop's code
  while (have_rows_to_output) {
    if (fmod($i, 2) == 0) { // it's an even number
      output_even_style_row;
    } else { // it's an odd number
      output_odd_style_row;
    }
    $i++;
  }
?>

http://www.nullislove.com/2007/05/09/zebra-striping/

This is a simple way to stripe alternate rows of output or to do  anything different as I process each alternate row. Typically, I set the <tr> element's class to "myEvenRow" or "myOddRow" then output the <tr> data just after the IF statement.

I found this full example at nullislove.com. The page also has a Ruby example. Full props to them.

Output zebra stripe rows in PHP

color

PHP