Depending on the template you have chosen, the page may be generated with no explicit body background color. Because different browsers have different default background colors (usually either white or gray), you should be sure that the page is generated with an explicit background color of your choice, so that your page will appear as intended for all viewers. When in doubt, use white, as shown below, for maximum contrast with dark text, to be most easily read.
Login and navigate to the page whose background color you want to specify. Select "Work on this Page" or "Work on this Page (All Changes)."
Click on the "Manage" button in the content-spanning toolbar; select "Page Margins Colors and more ..."
Click in the data entry box to the right of "background"; in class, type to replace the existing "#FFFFFF", changing it into "#FFAA55" (without the quotes, but be sure to include the initial pound sign).
You could also choose to specify a background image, instead of a background color. If you do, be sure to choose an image that will "tile" gracefully whenever the browser is using a window bigger than the image.
Click on the "Save" button.
The background color change takes effect immediately, with no need to submit for publication or to seek approval, and is not recorded in the Version History, so it can be restored only by re-doing the above steps.
Restore the background color to white by re-doing steps 2 - 4, specifying "#FFFFFF" in step 3.