If you only need a background on a certain page, the easier way is to
draw a text box or rectangle that fills the selected page, right-click
on the text box or rectangle, format it with no line color and the fill
color of your choice, and format it as "behind text". You can do this
to each of several pages if you want.
Alternatively, isolate the selected pages with section breaks, and
format the section with the desired background fill.
