Q: What is the difference between black shamans and white shamans?
A: According to Shamanism: a cross-cultural study of beliefs and practices by Gary Edson (at p. 74) “White shamans served heavenly deities and black served interests of the underworld (and deities)”.
JAPANESE MYTHOLOGY & FOLKLORE 
‘Black’ & ‘White’ Shamans
As well as the different types of magical practitioner, the shamans were also divided into two separate, but sometimes overlapping, categories – ‘black’ or ‘white’ shamans. The former were regarded as the most powerful of the two and were sometimes known as ‘warrior-shamans’ because they battled evil forces and were consulted as military advisors. They obtained their power from the north (possibly the North Pole or the North Star) and could be easily identified as they always wore black robes with very little, if any, decoration. The primary function of the black shaman was to deal with demons and the dark gods on behalf of their clients. In this role they were hired to curse their enemies and blight their crops and livestock.
In wartime the black shamans attached themselves to the army rather like the modern padres and helped to win battles using their occult powers. In peacetime they took a more positive role as diplomats, political advisors and emissaries and they oversaw the preparation and signing of treaties with the appropriate magical rites. Black shamans were greatly feared, even after their deaths. In the 19th century when a famous one died she was placed in a coffin made from the ‘unclean’ wood of an aspen. Her corpse was then nailed down with aspen stakes so she could not become a ‘night walker’ and haunt the living.
In contrast, the so-called ‘white’ shamans obtained their magical power from a westerly direction, the home of the benevolent deities and spirits. They operated at a tribal level almost exclusively as healers and diviners and they only had dealings with beneficent entities. It was their role to pacify angry or evil spirits, exorcise them if they possessed human beings and help the tribe live in harmony with their natural environment and the spirit world. To this end on a physical level they were often employed in an administrative role to oversee tribal affairs
Is there any connection to the idea of black witches and white witches (healers)? Do you think? An ancient cultural diffusion across Eurasia?