Lightning App Manager branding and navigation
Key Takeaway
You set a Lightning app's branding and navigation in the App Manager. An app's own brand image and navigation bar color always override the Lightning Lite and Lightning Blue themes, even when the theme override option isn't selected.
A Lightning app is a bundle of objects, tabs and other items. Users open it from the App Launcher and work in it through its navigation bar. You create and edit Lightning apps in the App Manager in Setup. There you set the app's branding (name, color and logo) and its navigation (which items appear, their order, and standard or console navigation). You also decide who can use the app and how much users can personalize it.
What a Lightning app is
An app is a collection of items that work together for one purpose. A Lightning app puts a set of objects, tabs and other items into its navigation bar, so a group of users has what they need in one place.
A recruiting team works with two custom objects, Candidates and Job Openings, plus Reports. You build a Recruiting app with those three items in its navigation bar, a teal color and a handshake logo. You give the app only to the recruiter profile. Recruiters now find Recruiting in the App Launcher, and other users don't see it there.