The Anahat-Chakra is located at the level of the physical heart, behind the spinal column at the center of the chest. Like all other chakras it is not a physical but an astral center. When I meditate on my chakras and move up and down through these levels in myself I see the different colors with my own eyes.
Meditation based only on colors can result in serious disturbances of consciousness.
I have heard of numerous such cases. Some people who come to Yoga are disturbed and unstable and that is not obvious at first glance. In time these disturbances come to the surface and then people think it is Yoga that caused it. Colour meditation by itself is dangerous in any case because it changes the state of the thoughts and of consciousness. When colors do come up in meditation they should be neither sup pressed nor clung to.