The final main chakra is Sahasrara Chakra, the Crown Chakra at the top of the head. It is envisaged as a thousand-petaled lotus, and its color is white, because white is comprised of all the colors of the rainbow. All of the effects and benefits of the other chakras are encompassed in Sahasrara, considered the most subtle of the chakras, symbolizing pure consciousness. This chakra is no longer concerned with the "earthly" things of the lower chakras. In Kundalini Yoga, when Kundalini energy finally reaches the Crown Chakra, Samadhi-Enlightenment-occurs. Samadhi is considered union with God, full absorption in the Divine. Yoga is the philosophy behind major Eastern religions Hinduism and Buddhism, but the idea of absorption in the Divine is central to the mystical traditions of all faiths. I am actually doing research now on a work I plan on the "Yoga" of St. Theresa of Avila.
As you can see, the chakra system moves from the "earthly" realm, beginning with the literal element of earth in the Root Chakra, all the way up to the "heavenly" realm of the Crown Chakra. This symbolizes the mystical journey one undertakes when attempting yoga. The yogi begins with the physical body, with the asanas, and from there moves forward on the spiritual journey toward enlightenment. Each chakra is a step on this journey. For example, we can stimulate the Third Eye Chakra with Tratak, steady gazing. Tratak leads eventually to true meditation, which stimulates the Crown Chakra. Meditation, prayer, devotion to God (bhakti), and works of mercy are the way to engage the Sahasrara Chakra.
As always, special thanks to Anodea Judith, the foremost expert in the chakra system.