Customize notification led color without app How can you customize the color of the notification LED (i.e. specify the rgb value) without using an app?

Does this require rooting? And if it does, what setting would then be used to do this?

Is there a way to manually control it? For example make it color cycle on demand for a neat effect?
There is no Android built in feature or setting to do this. There are public APIs for it. There are many apps for this.

Certain OEMs such as OnePlus (and Moto ?) allow customizing the LED color per app.

There may be diagnostics pages on certain devices (I remember the old Nexus S had something like that) where you can type in some code on the dialer to run them, then do some diagnostic related things. I don't know if such things are still being shipped. Either way it is for diagnostics purposes only and are quite well hidden.