What does protection from [quality] do?
Yes, Day of Judgement will destroy a creature with Protection from White. 

(from AlexP) No, Elite Inquisitor cannot be blocked by Zombies. Elite Inquisitor can, block Zombies normally. If a Zombie would assign combat damage to him, it is prevented and he takes no damage instead.

Protection from {quality}, grants four different things that can be easily remembered from the acronym, DEBT. 

Creatures with Protection from {quality} cannot be:


D amaged, by sources with that quality (the damage is prevented).
E nchanted / E quipped / Fortified, by cards with that quality.
B locked, by creatures with that quality.
T argeted, by spells or abilities from sources with that quality.