This is a mini guide on how to change the background color of IPB. I am answering this question as a lot of new users that I have found are looking for some quick edit of the background color.
First go to your admin control panel > Looks & feel > %choose your skin% >
On your drop menu button which is located on the far right corner and choose Edit Colours (CSS Easy Mode)
On this page you will find a section called body this section is for the whole content of the page. Under that there is a text box named other css attributes in there there should be a something like below:
background:#FFF
Now to change the color of the background you have to change the #fff to something else. To find the right hex color I recommend you give a visit to colorblender. Once you have found the color, there should be a small field below the color saying HTML #000000 just copy the hex and replace the #fff in the field above.