The Colour suggested was for your overall background colour, not the centre section where the product images and descriptions live; however
If you would like to bulk edit your fixed in-line style, use Dreamweaver:
- Ctrl+F
- Find in: Folder... select folder
- Find: background: #fff;
- Replace: background: transparent;
- Replace All
NOTE: Dreamweaver will re-write all the files on the fly and save them, so PLEASE make backups before trying that out.
3/4 are examples, but I'm sure you got that.
To get the sidebar completely black, you could use a background image in the correct div to touch up where you have padding issues.
As long as the over lying divs are set to "background: transparent;" the touch-up background image will show through and make the whole sidebar show whatever colour you specify with your CSS / image combo.
At the end of the day, the site is perfectly usable and has some nice features as it is - I would concentrate efforts on continuing the SEO development, as you seem to have a good grasp of what's required. Nice site :)