Color coding when shifts are open or filled

This is useful because when viewing shifts for the day or week, the shift boxes are always one color whether it is open or fulfilled. This way if there is an open shift that needs to be covered, there will be a clear visual indicator.

In the situation where a volunteer drops from a shift, the shift box would turn bright red (or whatever color the manager wants it to be) to know that they have an open shift to cover. When the shift is being covered, the shift box would change their color to when a shift is filled.