Change logo in email with Frosty theme

Hi, quick question. How can I change the logo that is sent in the welcome email (when a new user signs up) when I am using the Frosty theme.

I found this resource http://docs.stackideas.com/administrators/templating/customizing_email_logo, but it explains how to do this only if you are using the default wireframe theme. I'd like to be able to change the logo and use the Frosty theme.

Thanks,
Colt