Color Psychology & Color Theory.

Some occultists tell of an astral world where spiritual culture reigns supreme. It is inhabited by the nature spirits of Paracelsus, the undines (water spirits), the sylphs (air spirits), the gnomes (earth spirits), and the salamanders (fire spirits).

In Panchadasi's book, this world is described as having seven planes graded according to degrees of vibration. [Faber Birren]