The concept of chakras has been around for centuries, with evidence of its existence found in the oldest Indian texts, the Vedas, dating back to 1500-500 BC. The chakra system was also mentioned in the Shri Jabala Darshana Upanishad, the Upanishad Cudamini, the Yoga-Shikka Upanishad and the Shandilya Upanishad. According to Anodea Judith, author of The Wheels of Life, knowledge of the chakra system was passed down through an oral tradition by the Indo-European people, also known as the Aryan people. Although the chakra system was traditionally an Eastern philosophy, it wasn't until New Age authors such as Anodea Judith began to write about it that it became more widely known and accessible.
This is when the idea of associating rainbow colors with each chakra was introduced, a modern Western invention.