black
Black is somehow the true center, the sum of all the rays, including the seven corresponding to the rainbow.
Some initiations of the Islamic tradition include 7 or even 8 steps, the latter being black, a sign of accessing the final step of spiritual fulfillment.
Therefore, black symbolizes the manifestation of the cycle or the Principle and end of the cycle. Consequently, black represents both the brightest and the darkest light: non-manifestation and manifestation.
https://www.insightstate.com/spirituality/spiritual-meaning-of-colors/
