Facebook dispatches an application which is called a Facebook messenger. It is basically used to visit with colleagues. Undoubtedly, you can use it with your flexible number. There is a faint mode available which is sensible to use in the night. It is on a very basic level developed to improve the vision. For the Facebook application, there isn't any full diminish mode, yet you can start it from your phone's settings. For extra, contact Facebook customer service .