An extremely large proportion of people looking to update their bathroom ceiling will opt for a white finish. This is the lightest and most reflective option and also ties-in with more traditional ceiling coverings which in the main have always been white (until the mould sets in!)
Choosing a plain white ceiling will give you that traditional look but will provide you with all of the advantages of a modern panelling system.
Matt white cladding is the nearest you will come to emulating a painted plaster ceiling while gloss adds a little more reflection and is an easier surface to wipe over (though not by much).
As well as plain white, ceiling panels can also use white as part of other designs such as white wood-grain effects or used with silver or chrome strips to break up the solid colour.