Bug in Ereg?

Hi, I have a form with checkboxes that POSTs to a PHP script. What is posted [ from phpinfo() ]: _POST["color-1"] on _POST["color-4"] on _POST["color-6"] on Parser: foreach($_POST as $ThisVar=>$ThisVal){

       if(ereg("color-", $ThisVar) AND $ThisVal=="on" OR $ThisVal==1){
           $newVarA=explode("-", $ThisVar);
           $colors.="$newVarA[1]:";
           }
       }

Expected Output: $colors="1:4:6:"; Real Output: $colors=":1:4:6:"; I can work with the output I am getting, however, I am curious why I am not getting the "expected output". Can anyone shed light on this? I am using PHP 4.3.2 compiled under a unix environment. Is this a bug in ereg or am I just not seeing something obvious in my foreach? Thanks, Kris