In MS Word, the users can change the background color of the page. 

A 'w:background' property is applied to the whole document in DOCX, and this property is used as a page color in Paged layout mode, and as a background color in Web layout mode. 

When implementing, think of whether RadRichTextBox.Background should be synchronized with this property when RadRichTextBox.DocumentInheritsDefaultStyleSettings is true.

Workaround: Currently, background could be set using RadRichTextBox.Background property in Web layout mode, and using a custom style, as described in When the LayoutMode is Paged the Background forum thread, in Paged layout mode.