Zohar 1:18b

These are the colors that are seen in that image [of the glory], white, red, and green. “Such was the appearance of the surrounding radiance” (Ezek. 1-28)- the light that is hidden in the rotation of the vision of the eye. “That was the appearance of the semblance of the Presence of the Lord” (ibid.)- the colors that are united in the lower unity according to the unity that is united in the upper unity. [The words] “YHWH, our God, is YHWH” (Deut. 6-4) [designate] the hidden colors that are not seen and which are bound to one place, one unity above. The colors in the rainbow below which are united in it, white, red, and green, are like the hidden colors. They constitute another unity, the secret of “and His name is one” (Zech. 14-9), “Blessed be the name of His glorious kingdom,” the unity below. The upper unity- “Hear O Israel, YHWH, our God, YHWH is one” (Deut. 6-4), one parallels the other.

Translated by Elliot Wolfson in Through a Speculum that Shines- Vision and Imagination in Medieval Jewish Mysticism, Princeton- Princeton University Press, 1994.