You can set your phone to flash your camera light, your screen, or both when you receive a notification (including calls) or an alarm sounds.
To flash the camera light, turn Camera flash on 
You can't change the color of the camera light.
To light up the screen, turn Screen flash on 
If you want lights to show on the edge of your phone when you receive notifications, you adjust those separately, in Settings > Display > Edge Lights. Learn more.
If you turn on Do Not Disturb to temporarily silence notifications, the lights will stay dark as well. When you see 