I cannot change the background of my PAGES page

Hello!

I've read through all the other postings and I am unable to change the background color of my PAGES document. If I use a shape and fill in the color, it covers up all the work i've done. I've tried going under the HELP menu, as suggested, and looking at "create or modify a layout" and had no luck there either. I've also tried to go to INSPECTOR then GRAPHIC and choose fill but it won't allow me. I am at a loss! I've gone too far in my PAGES document to start again and lose all the work I've done but the plain white background isn't doing anything for me. ANY help would be so appreciated. Thank you!