Split word by space or plus character to array.

$arr = preg_split("/[s,+]/", trim($_GET['text_search']));

 

And call function markWord for replace hightlight styles.

function markWord($arr,$str)

{   

$x = sizeof($arr);

for($i=0;$i<count($arr);$i++)

{

      $mul = ($i+1)/$x;

      $str = str_replace($array[$i],'<span style="background-color: '.rand_color($mul).'">'.$array[$i].'</span>',$str);

}

return $str;

}