*My edge lighting for notifications is working perfectly on my T-Mobile Note 8...
Just Follow these steps exactly;
(1) Click Settings, Click Display, Click Edge Screen, Click Edge lighting (mine is on Always). Click on the Word Always to enter sub menu.
(2) Click Manage notifications, Choose what you like, I have Messages, WhatsApp, Email, and Gmail selected. Back out one page.
(3) Click on Advanced Settings, Highlight Custom color Then click on the round DOT to the right of the word Custom color, Setup your cutom colors choose done, then back out a page and set Width all the way over to the right and leave Transparency on Low.
(4) Top right of page press Preview, when your happy with your color back out one screen. At the very top of this screen make sure that Edge Lighting is set to "on". After that back all the way out Your Done!
*Notifications have to be setup like this to work as there not album color. Do exactly what I wrote and you guys should be fine.