If you are planning to publish your project to HTML Help (CHM) you will also want to configure the appearance and features of the Microsoft help viewer used to display this format. These settings are stored in what is known as a "help window definition".
You can also define background colors for your topic pages and topic headers. These colors are defined in the HTML page templates for HTML-based publishing formats. You cannot define topic and header background colors for PDF, Word DOCX or printed manuals.
The settings in Help window definitions are only relevant for the Microsoft HTML Help format. For details see Help Windows and Help Windows Settings in the Reference section and Choosing a help window in the Creating Topic Files section.