Theming the buttons in the clean theme

Is there any way to theme the buttons in the ReCaptcha box? I'm using the "Clean Theme" and I can sort out the borders and field colours with a style sheet, but the three images for reload, audio and help seem to be pulled from the Captcha server without any way to override the settings.

The three images are:

• https://api-secure.recaptcha.net/img/clean/refresh.png
• https://api-secure.recaptcha.net/img/clean/audio.png
• https://api-secure.recaptcha.net/img/clean/help.png

Not a big deal, but it's the last item in my theme which doesn't have the requested colour scheme prior to going live and putting up images, and I've been puzzling over it all day. Example is at: http://www.reachinsurance.co.uk/content/callback