Lucid comes with two master pages. This article briefly explains the differences between the two, and how to edit them.
Main Master vs Projects Master
You can tell when a page has a master applied by looking below the page name. If a page has no master, it will say [No Master] below the page name.
The 'Main Master' page is applied to all pages. By default, whenever you create a new page, the Main Master will be applied to it.
The 'Projects Master' page is used specifically for the pages under 'Galleries and Projects'.
The 'Projects Master' page has the 'Main Master' applied to it. This means that whenever the 'Main Master' page is changed, the changes will be applied to the 'Projects Master' page. The 'Main Master' is applied to the 'Projects Master' so that the 'Projects Master' still has the same consistent appearance (menu, navigation, etc) as the 'Main Master'.
Having a 'Projects Master' page allows you to have a master page that will only apply to pages with 'Projects Master' applied to it. In the template, it is used to create a consistent navigation for the Gallery and Projects pages.
Editing the Master Pages
To create a change that will apply to all pages, make the change on the Main Master page.
To create a change that will only apply to the pages under 'Galleries and Projects', make the change on the Projects Master page. Note: objects on the 'Main Master' cannot be edited from the 'Projects Master' page.