Color has played a part in many magickal systems. Color possesses energy, and like any other energy it can be used in a spell. In India and China, color magick goes back thousands of years and color energies have been used to aide in healing. The symbolic energy centers of the human body, known as the Chakras, are said to be ruled by colors from red at the Root or Base Chakra to the dark blue of the Third Eye and pure white at the Crown. In the Hebrew tradition, the mystical realms or sefirot of the Kabbala are also linked with colors and, as with the Chakras, Kether, the Crown or topmost realm is white.
These ancient beliefs have been found to have psychological and physical validity. For example, blue helps to lower blood pressure and steadies respiration, while red raises the metabolic rate and orange stimulates the appetite and aids digestion. Pink is sometimes used to create soothing environments in prisons and hospitals as it seems to reduce aggressiveness and anxiety, although this effect can be counter-productive after prolonged exposure.
Colors are also associated with different planets: orange or gold for the sun, silver or white for the moon, yellow for Mercury, red for Mars, blue for Jupiter, green for Venus and black for Saturn.
The correspondences given here and in most other spell books are based on a consensus of the majority based on the experience and experimentation of those who practice magick, those who use color for forms of healing therapy, and studies done to determine how colors influence the psyche. However, you may find in your personal practice that a color that works well for others does not for the same purpose. It is advised to do some experimentation of your own. The following exercise is from Arin Murphy-Hiscock's book, Power Spellcraft for Life:
Create your own color chart to accurately reflect the power which color holds for you. On your next trip to the hardware store, grab a handful of paint chip cards. Make sure you have at least the basic colors such as blue, green, red, yellow, orange, purple, brown, pink, white, and black. Bring them home and cut them up into separate chips. Glue the chip to the blank side of an index card. Meditate on the color for awhile. Gaze at it and write down all the feelings it evokes and the associations the color has for you on a blank piece of paper. Don't do the whole pile of chips at once; do one or two per day. When you're finished, copy the feelings and meanings each color has on the lined side of the appropriate index card. You now have a set of reference cards for your own personal color correspondences. Keep them in a recipe box decorated to your taste, or punch a hole in a corner of each card and string them onto a ring or tie them together with a cord.