Lead Developer
Perfect! You can also use the page ID.
As for the colors, if you want individual pages to have different styles for all of these elements, you will have to write the CSS for it I’m afraid. The add-ons work globally, but not on a per-page basis.
These are some of the elements:
Header: .site-header
Navigation: https://gist.github.com/generatepress/793804f553c25c70823c (you will have to add the page class before all of those instances)
Widgets: .widget
Footer widgets: .footer-widgets
Footer: .site-info