Tattva vision

 
Tattva vision is a technique developed by the Hermetic Order of the Golden Dawn to aid with the development of the faculty of astral clairvoyance. They were probably derived from the elements, or Tattva [also known as Tattwas], of the Samkhya version of Hindu Philosophy.
The tattva symbols.
The astral forms of the "tattvas" and equivalent in Western elements:
Akasha - Spirit
black or indigo "vesica piscis" or egg
Tejas - Fire
red equilateral triangle
Vayu - Air 
blue circle
Apas - Water
purple half circle / silver crescent
Prithivi - Earth
yellow square
Constructing tattva cards.
"Tattva cards" can be constructed by cutting the tattva symbols out of coloured paper or card, and pasting on to small cards of about 6 inches by 6 inches in size. Alternatively the tattva symbols may be painted onto the cards, or a commercial set of cards may be obtained.