Stormtrooper armor protects its wearer from many hostile environmental conditions: extreme heat, extreme cold, toxic gases, and even short periods of exposure to the vacuum of space. In addition to acting as a full NBC suit (as seen in ANH when two stormtroopers were seen surviving the vacuum of space), it protects against physical threats such as shrapnel and blaster bolts. Due to the sheer firepower of blasters, however, the protection that any armor can offer is limited; the armor cannot fully protect its wearer from a direct hit, although it may mitigate the damage.
Stormtrooper armour is specifically described as being impervious to projectile weapons, but this claim isn't entirely accurate; the white, rigid components are resistant to projectile small arms, but projectiles can still reach the wearer through the armor's joints.
Equipped with built-in air filters, vision enhancers, targeting systems, suit environmental controls, communications gear, and 20 minutes of emergency oxygen supply, Stormtrooper armor offers various features to aid in combat situations.
We clearly saw camo-armor in the Imperial ranks in ROTS.
Stormtrooper Armor in Debates
Some idiots try to use physical impacts knocking troopers over as evidence the armor can't be bulletproof, but that only shows their lack of understanding of momentum. No armor can violate conservation of momentum. The momentum is still transferred to the target regardless of the strength of the armor. Consequently, if you're wearing a helmet in real life and get hit in the head, you can suffer a head injury even if the the helmet remains intact (hockey players have been known to get concussions from impacts that don't damage their helmets).
Clone Trooper Armor
Clone Trooper armor is the predecessor to Stormtrooper armor. It is confirmed to be a sealable suit that will allow the wearer to operate in a vacuum for at least several minutes. It is also confirmed that wearers can potentially survive multiple hits from blasters and still continue to fight, although the blaster's power setting is presumably a factor.
First Order Armor
First Order armor is based on Imperial Stormtrooper armor, but it does not have all of the same features (as standard issue, at least). For example, standard First Order Stormtrooper armor does not have the same breathing protection as earlier armors: First Order armor filters out particulates, but it doesn't filter out toxic gases.