I have read this: http://www.appnitro.com/forums/topic/captcha?replies=2#post-297
I have modified the file accordingly, and have the correct form- since I only have one form, form id 1, my code is as follows inside the custom_hooks.php file:
`
function form1_hook_pre_captcha(){
$capthca_theme =<<<EOT
<script>
var RecaptchaOptions = {
theme : 'clean'
};
`
No matter what, the default, 'red' theme appears..