In response to a post in another thread I thought I'd highlight some of the customisations that cane be made to the appearance of the Google reCAPTCHA.
Firstly there are 4 different styles supplied by Google:
White

Red (Default colour)

Black

Clean

To use these just include the following script on the page
Code:
        <script type="text/javascript">
            var RecaptchaOptions = {
                theme: 'white'
            };
        </script>
Additionally it is possible to style the individual elements through CSS. The following changes the font of the 'Type the two words' text
Code:
.recaptcha_only_if_image {
color:red !important;
font-size:1.4em !important;
}


There are many more customisations available see this Google page for more information, or just post here and I'll be happy to help.
Regards
David