Wordpress theme - ASAP

Hi, I'm looking for someone who is very comfortable with wordpress and want them to create a theme for us.? We have very specific requirements and very good idea of what we want. The problem is we'd like to have this done by tomorrow, what I think can be done is take an existing theme and just modify it (essentially the color scheme and some of the graphics).? It appears most of the wordpress themes are just css - so that is a requirement that you can modify the css to make the site work. I want to be able to take the theme you create and just plug it into wordpress and have it work.