Armor customization

"Armor Permutations" is a feature in Halo 3, allowing the player to aesthetically customize his/her multiplayer character.

Introduction
Armor Permutations allows a player to customize his/her multiplayer character as either a UNSC SPARTAN-II or a Covenant Elite, and change between different helmets, shoulder pads, chest armor, and detailed colors (primary color, secondary color, and armor detail). All permutations are aesthetic only and do not change gameplay.

They were originally discovered in the Halo 3 Beta hexadecimal code by modders and were confirmed to provide high levels of player customization by GamePro's June magazine issue. There are "thousands" of possible combinations.

Armor Permutations are unlocked by accomplishments in either the campaign or multiplayer modes of Halo 3.

SPARTAN Armor Permutations
There are a wide variety of SPARTAN armor permutations, with 12 helmets, 8 shoulder pieces, and 8 chest pieces for a total of 5,376 different SPARTAN armor permutation combinations: one helmet, two shoulder pieces, and chest piece per permutation.

Helmets

 * Mark VI: Default Unlocked
 * CQB: Default Unlocked
 * EVA: Complete Campaign on Normal, Heroic, or Legendary
 * EOD: Complete Campaign on Legendary
 * Hayabusa: Collect all skulls
 * Security: Get all achievements in Halo 3.
 * Scout: Complete "Used Car Salesman" Achievement
 * ODST: Complete "Spartan Graduate" Achievement
 * Mark V: Complete "UNSC Spartan" Achievement
 * Rogue: Complete "Spartan Officer" Achievement
 * Recon: Bungie Employees
 * Flaming Helmet: Bungie Employees only

Shoulder Pieces

 * Mark VI: Default Unlocked
 * CQB: Default Unlocked
 * EVA: Complete The Ark on Normal, Heroic, or Legendary
 * EOD: Complete The Ark on Legendary
 * Hayabusa: Collect 9 skulls
 * Security: Possibly getting 39 achievements.
 * Scout: Complete "Mongoose Mowdown" Achievement
 * Recon: Bungie Employees

Chest Armor

 * Mark VI: Default Unlocked
 * CQB: Default Unlocked
 * EVA: Complete Tsavo Highway on Normal, Heroic, or Legendary
 * Hayabusa: Collect 5 skulls
 * Katana (Add-On) : Earn 1000 out of 1000 Gamerscore Points for Halo 3
 * EOD: Complete Tsavo Highway on Legendary
 * Scout: Complete "Too Close to the Sun" Achievement
 * Recon:Bungie Employees

Elite Armor Permutations
There are a wide variety of Elite armor permutations, with 5 helmets, 5 shoulder pieces, and 5 chest pieces for a total of 625 different Elite armor permutation combinations: one helmet, two shoulder pieces, and chest piece per permutation.

Helmets

 * Combat: Default Unlocked
 * Assault: Default Unlocked
 * Flight: Complete Campaign on Heroic or Legendary
 * Ascetic: Unlock "Steppin' Razor" Achievement
 * Commando: Unlock "Overkill" Achievement

Shoulder Armor

 * Combat: Default Unlocked
 * Assault: Default Unlocked
 * Flight: Complete The Ark on Heroic or "The Storm" on Legendary
 * Ascetic: Unlock "Overkill" Achievement
 * Commando: Unlock "Killing Frenzy" Achievement (Still Bugged as of 10/21/07)

Body Armor

 * Combat: Default Unlocked
 * Assault: Default Unlocked
 * Flight: Complete Tsavo Highway on Heroic or Legendary
 * Ascetic: Complete "Up Close and Personal" Achievement
 * Commando: Complete "Triple Kill" Achievement