To change the color of only the custom title, do this. In the bit of code you add to functions.php, there is this line:
PHP Code:
$extratitle="$post[field5]<br>";
Change it to this:
PHP Code:
$extratitle="<font color=\"#FFFFFF\">$post[field5]</font><br>";
Of course, replace #FFFFFF with whatever color you want, using either the HTML #xxxxxx color codes, or an accepted named color.