Player Character

A Player Character (PC) is a character in The World who is controlled by a human player. These characters are distinct from Monsters, Non-Player Characters, and Vagrant AI, because they are controlled by a human at a Computer Terminal.
PCs are categorized by their Class, which determines what kind of Weapons and Armor they can equip. PC designs are determined by their class, which depends on the version of The World the character plays. Because there are only so many designs available for each class, some characters appear similar, if not identical.

By Version

The World

A PCs appearance is generally static, as their clothes remain visually unchanged when they equip or remove Armor. A PC's weapon will visually change depending on what they have equipped. There are also some special items that can change the character's appearance permanently, though these are very rare or, in some cases, illegal. The PC's in-game appearance is otherwise set at character creation and will not change unless the character is edited or acquires one of the aforementioned items. This changes in a later update, as seen in Legend of the Twilight.
In some media, clothes are shown to be affected by Battle damage, as seen in .hack//SIGN; during the opening and when Subaru is attacked by another player.
Some instances of notable character appearance changes include Balmung's Wings (rare item), Piros' color changes due to Mia's Love Potion (illegal item), and Kite's color changes due to the Book of Twilight (Illegal Item). Subaru also had a dramatic color change between when she first started playing and when we see her in SIGN, though how she changed her attire from Pink to Blue is not specified.