How to change the background-color within integrated phpbbforum?

Hi,

I'm using Drupal 6.10 and I have integrated phpbbforum module and phpBB3 into my Drupal site within a node.
I'm trying to change the default background-color (which is white) to some other color that will fit my entire site background.

As I found where to change it in the colours.css within the theme/prosilver/ folder but when I use ACP the color is always white... When ACP is disabled the entire note is not looking good...

Sorry for my English.

Can anyone help? Please...

Thanks,
Lebi