The word "White Women" (also called "Witte Wieven" in Nether-Saxon dialects) has nothing to do with colour, the word "white" is a misinterpretation of "wit", which meant "wise" (English "wit"=funny/clever, Dutch "weten"=to know).
Women who were concerned with fortunetelling and predicting the future were highly respected in Germanic society and many of them were chosen as priestesses, they were often refered to as "wise women" and after their death the people kept honouring them at their graves.
If mist appeared around such a gravehill the people believed that this was the spirit of the wise woman who had returned to the land of the living, the people would then bring offerings to her spirit and asked her for help, a custom that was common in Germanic religion and was related to the honouring of Disen, Land wights, and Alfen.
The belief in White Women probably originates from the custom of honouring the spirits of "wise women" after their death, another possibility is that the White Women originate from the belief in Disen, Land wights, and/or Alfen; in both cases the belief must be of a very old origin.
In some areas in Belgium and the Netherlands the White Women were also called "Juffers" or "Joffers", which means something like "ladies", in other areas they were refered to as "Alfen" or "Alven" and there was also the belief in the "Alvinne", which was a ghost in a white cloak, an 18th century word for magic and witchcraft was "Alverij", this names all point to a possible connection between the White Women and the Alfen.
The "White Women" belief can be found throughout northwestern Europe, especially in the Netherlands, Belgium, and France; in France they were known as "Dames Blanches" and they were mainly seen in the area of Lorrain (Lotharingen) near the German border.
The belief in White Women was especially strong in the eastern (Saxon) provinces of the Netherlands; the Hunebeds in Drenthe were seen as homes of White Women and even in the 19th century AD there were still farmers who believed in White Women.
In the village of Zwiep near the city of Lochem in the Achterhoek is a park for children that uses the White Women as its theme, it is called "Uitspanning de Witte Wieven" and children can go there to play, hold parties, and there are even guides who lead groups through forest trails telling them stories about the White Women, there are straw puppets of White Women in the park and now and then actors dressed up as White Women appear between the trees after which the guide asks the children to scare them off, the "White Women" then quickly run away, I have been there myself when I was a little boy and some of the actors were performing so well that they scared the hell out of me ;)
The White Women were believed to live in or around hills, gravehills, swamps, pits, forests, lakes, stones and other objects of nature and the sound of the wind was often mistaken for the sound of White Women mowing the grass with their scythes or operating their spinning wheel, at night they came out of their holes and floated trough the forest, they plucked leafs and flowers which they littered troughout the area.
After the Christianization of Europe the White Women were depicted as evil witches and they changed from wise female spirits into servants of Satan, they tried to harm people who were lost in the woods and they could only be scared away by hissing at them, many local legends about the White Women were changed to demonize them, but in a lot of folktales the originally positive character of the White Women remained.
During the Middle Ages the church ordered the people to bury their dead in the holy ground around the churchbuilding instead of burying them out in the field, eventually the people started to obey this new rule but in many places the funeral procession was first led along an ancient gravehill or other place that was associated with the old heathen religion before the procession went to the church.
The Christian rulers did not like this of course and they established the so called "death-roads" over which a dead body had to be brought to the church, this death-roads kept the people well away from any gravehills or other heathen sites of course.
Another tactic they used was demonizing the beings from the old heathen religion by making up stories about them, the White Women for instance were accused of killing innocent people, worshipping Satan, violating men, and stealing babies which they kidnapped to their den, etc. there are even stories about people who could hear infants crying at mounds and holes that were connected to White Women.
In later Medieval folklore there were also stories about White Women who were seen dancing and carrying objects like bloody whips, petchtorches, and bloody handkerchiefs, White Women seldom appeared alone and were mostly seen in groups of 2 or 3 individuals, nowadays they are seen as witches and they are often depicted with broomsticks, pointy hats, and long noses, but the original White Women were good spirits of nature; they were a part of a beautiful and ancient culture that has been unrightfully perverted during the Christianization, I hope that the people will one day realize what treasures they have thrown away.
If you would like to read some legends about White Women I advice you to take a look at the legends on this site.