Chakras are centres of energy which govern certain zones of the body; they convey energy between dimensions (or planes of existence) and are centres of subtle forces, the generation of prana (energy) and higher consciousness.
Visuddha is located in the neck. The lotus petals, of which it has 16, are grey or silver (sometimes a smokey purple).
These petals contain seven notes of the musical scale, poison and nectar, and seven “calls” used for exorcism, sacrifice, fire ceremonies, self-determination, blessing and exaltations.
Associated with the power of projection or expression, this suggests the beginning of priestly or occult powers.
This chakra is also associated with conquest of the ethereal state of matter which governs the expressive mind. Visuddha is an expression of creative activity and inspiration, along with the ability to receive nurturing and connecting with the inner source of grace: the inner giver and receiver are one.
Energising this chakra involves devotional practices such as ritual, prayer, chanting, using sound vibration and creative expression.
The god of this chakra is Siva in a half-male, half-female form (Ardhanariswara) sitting on a white elephant accompanied by the yellow Sakini Sakti (goddess) with four hands. Whereas he has mastered diverse knowledge, she reigns in the lunar region, over the minor mysteries.
Visuddha controls both arms and is the centre of sense-withdrawal (pratyahara). Through concentration on Visuddha, one loses sensitivity to heat, cold, pain, pressure, touch and temperature in the arms. The tantras say its instrument is the ears, used in such a way that the sounds of the world are not distracting and only one sound is heard: nada (a less intense sound of Om) or the name of God.
Meditation on this chakra brings one to the threshold of liberation.
Information source: Energies of Transformation, A Guide to the Kundalini Process, by Bonnie Greenwell PhD.