I'd probably run the result text through a [man]preg_replace/man, having it replace the searched word(s) with the word surrounded by a <span> tag that includes a class, and in your CSS stylesheet or <style> block assign the desired color or other effect to that class.
$text = preg_replace('/\b'.$searchTerm.'\b/i', '<span class="search">\\0</span>', $text);
CSS:
.search {
color: #c00;
background-color: #ff9;
}