iOS 9.3 is coming in the Spring and will introduce Night Shift as well as a number of other new features.
Apple Releases iPhone OS 4.1 Beta 2 to Developers
Apple has released the second beta for iPhone OS 4.1 to developers. The first beta was released two weeks ago and introduced some minor new features. Today's beta seems to only add minor bug fixes into the mix without any notable other features.
The iPhone 4 proximity sensor issue does not appear to be fixed in this latest beta. Apple has said the proximity sensor will be addressed in a future software update.