For books made in the older creation studio (mstudio): To change the layout of your pages, select the "Layout" option from the panel on the left. Then drag and drop the layout on the page in the book where you'd like to change it. You can also filter the layouts by the number of photos per page by clicking the drop-down menu.
You can change the background colour the same way, by selecting the "Background" option from the menu (at the bottom of the page) and then dragging the colour you want to your page.