[otrs] How to change the default theme for Customer interface?

Hi all, we are implementing OTRS 2.2.6 in our company to give service support for our customers. A question about theme customization: which is the right way to make our theme the default theme so that when any user accessing this url: http://otrs.ourcompany.com/otrs/customer.pl can see our company theme with logos and colours? We have already implemented our theme and it is visible *after* the customer has logged in, but we'd like to make it visible even before :-) Thanks in advance. Regards, Luca