For a long time, I've tried to reconcile the Rainbow layer of the Loagaeth Circle with the Walls of the Sacred temple in the mandalas. The answer was right there, the buddhist's rainbow only has five colors. The cakrasambhara-tantra teaches that the walls of a mandala should be painted in these five colours.
This also leads into interesting comparisons of the rainbow of the magus to the powers of the rainbow body (also known as the body of light) of the buddhists.
These Bodhisattvas, from the realms of substances, non-substances, and non-thoughts, by the aid of Samadhi Power, had produced the Wisdom Fire, which burnt off their substances, desires, and non-brightness, and transmuted what they had relied on. They had tfore achieved the Wisdom Concentration, and attained Mind-Created Bodies, which are adorned by mighty supernatural powers. Such bodies are free of any interspaces, bones, or substances, they are like the sun and the moon, like rainbows, electricity, finest gold, luminous pearls, Sphatikas, Pravadas, Hridaras, Campakas, Pavonine Flowers and Moons, and the images from mirrors.
Such Bodhisattvas, by virtue of cultivating the causes of non-leaking when they were staying in various stages, had achieved Self-Mastery through Samadhi. They had been practicing the ten endless vows and transferred their merits, so that they attained such specially supreme bodies and are able to arrive this Secret Sublime World.
-Mahayana Secret Sublime Sutra 大乘密嚴經 Taisho Tripitaka (0681, 0682)