Zohar Terumah 44

All colors are good for a dream, except for Techeiles, like it was said (139a). Because it is the Kisei (throne) to judge the dinim of neshamas. And this level (or one level) is white. But at the time that it stands in the dinim of the nefashos, then it is the color Techeiles. And this was already explained.

At the time that a person sees this color, he remembers to do the mitzvos of his Master. Like the Nechash HaNechoshes, that when they would look at it, they would have fear before HaKadosh Baruch Hu, and they would guard themselves from all sins. And at the time that that fear of HaKadosh Baruch Hu came upon them, immediately they were healed. Who caused them to have fear before HaKadosh Baruch Hu? That snake, that strip that they were looking at. So too, Techeiles—“And you shall see it and remember all the mitzvos of Hashem” (Bamidbar 15:39)—from that fear of Him. And because of this, Techeiles is in the Mishkan.

Rabbi Yitzchak said: That which the master said—that Techeiles is the Kisei HaDin—and when it is in this color, then it is the Kisei to judge the dinim of the nefashos. When is it in Rachamim? He said to him: At the time that the Keruvim turn their faces one toward the other, and they look face to face. When the Keruvim are looking face to face, then all colors are set right, and the color Techeiles turns into another color. The color green turns into the color gold.

(According to another version: white.) And because of this, through the changing of colors, it turns from Din to Rachamim, and also from Rachamim to Din, and everything is through the change of colors. Just like Bnei Yisrael arrange their setup before HaKadosh Baruch Hu, so too everything stands, and so it is arranged. And because of this, it is written (Yeshaya 49:3), “Yisrael, in whom I will be glorified,” through these colors that are included one within the other, which is the beauty of all of them.