According to traditional Japanese beliefs, all humans have a spirit or soul called a (reikon). When a person dies, the reikon leaves the body and enters a form of purgatory, where it waits for the proper funeral and post-funeral rites to be performed, so that it may join its ancestors. If this is done correctly, the reikon is believed to be a protector of the living family and to return yearly in August during the Obon Festival to receive thanks. However, if the person dies in a sudden or violent manner such as murder or suicide, if the proper rites have not been performed, or if they are influenced by powerful emotions such as a desire for revenge, love, jealousy, hatred or sorrow, the reikon is thought to transform into a yūrei, which can then bridge the gap back to the physical world.
Today, the appearance of yūrei in film and stage is somewhat uniform, instantly signalling the ghostly nature of the figure, and assuring that it is culturally authentic.
White clothing - Yūrei are usually dressed in white, signifying the white burial kimono used in Edo period funeral rituals. In Shinto, white is a color of ritual purity, traditionally reserved for priests and the dead. This kimono can either be a katabira (a plain, white, unlined kimono) or a kyokatabira (a white katabira inscribed with Buddhist sutras). They sometimes have a hitaikakushi (lit., "forehead cover"), which is a small white triangular piece of cloth tied around the head.
Black hair - Hair of a yūrei is often long, black and disheveled, which some believe to be a trademark carried over from Kabuki Theater, where wigs are used for all actors. However, this is a misconception. Japanese women traditionally grew their hair long and wore it pinned up, and it was let down for the funeral and burial.
Hands and feet - A yūrei's hands dangle lifelessly from the wrists, which are held outstretched with the elbows near the body. They typically lack legs and feet, floating in the air. These features originated in Edo period ukiyo-e prints, but were quickly copied over to kabuki. In kabuki, this lack of legs and feet is often represented by the use of a very long kimono, or even hoisting the actor into the air by a series of ropes and pulleys.
Hitodama - Yūrei are frequently depicted as being accompanied by a pair of floating flames or will o' the wisps (Hitodama in Japanese) in eerie colors such as blue, green, or purple. These ghostly flames are separate parts of the ghost rather than independent spirits. (From: http://en.wikipedia.org/wiki/Yūrei )