To change the background color of a page, click on the "Background" button (located above the album design) on the toolbar. This will open a popup window where you can select a new color. Once completed, click done.
These steps also apply to changing the cover color of a Hard Cover, Paper Cover, Padded Cover, Silk Cover, Canvas Cover or Soft Cover photobook.
For more information on how to change default background color, please click here.