1. Alcove tub/shower with tiled walls: Use a vapor barrier, 1/2" CBU, and thinset. This is the second best option, but first for homeowner timid about floating a mortar bed.
2. Tub/shower ceiling: Use green board and a high quality latex paint
3. Tub/shower ceiling: Marble tile on ceiling - Can't be done safely by inexperienced homeowner.
4. Bathroom walls: Greenboard is better than blueboard/plaster.
5. If alcove tub tiles flange out of alcove to exterior face (for decorative purposes) it is OK to mount these tiles on blueboard/greenboard.
Love to have someone dispell any misconceptions before purchase/install.