Do demons have black hair?

The hair of a spiritual entity that is highly developed spiritually possesses great lustre and is a thing of great beauty. 

All such hair varies in shades and colours from the very lightest down to the shades of brown that still have a little sunshine in them, but does not extend to the darker shades of the brown—or to the black.

The hair of a highly developed spirit-life is of the finest possible texture and quality of spiritual material and possesses a lustre and beauty that cannot be described.

The refinement and development of the spirit-life can be told by the fineness, the quality, and the texture of the hair, and to some extent by its tints and shades and colours.

Fragments of Spiritual Knowledge Pertaining to the Spiritual World