In the Phillips HUE iOS 8 widget, you can add up to four different scenes to turn on without having to dive in to the HUE app, which is extremely useful. However, you still have to dive in to the HUE app to turn those lights off, or create a separate scene for turning the lights off and add it to the widget screen.
Solution: treat scenes in the HUE widget like toggle switches. When a scene is pressed, the system detects if the lights are already displaying that scene. If not, it will turn that scene on. If it is, it will turn the lights for that scene off.