I remember using an app on my Samsung Galaxy Nexus where you could set every notification to a different color, for every app. Cost me like $2. Last phone that had a notification LED (dunno if it was the Note 4 or Note 8) had only some basic configuration and the app was no longer maintained. Now, I don't have the LED anymore. Sad.
Maybe if I could have always-on display, but only with a virtual notification LED, I'd be happy.