Dear mkopek,
I am new to freelancer, but I have been working in CRM since 2005, and I know the code behind SugarCRM, so you can be sure that I will be able to manipulate the HTML and CSS to match your exact colour schemes.
I would propose to:
- create a development instance of Sugar 6.4.6,
- create the custom theme for you to examine and approve,
- then after backing up your live version, apply the new theme for you.
Kind Regards.