...anyone who keeps the obligation of tzitzit is as if he were admitted to the presence of G-d’s glory. This tells that tĕkhelet is similar to the sea. But the sea is similar to grasses, grasses are similar to the sky, the sky is similar to the Throne of Glory, and the Throne is similar to sapphire, as it is written (Ez. 10:1): “I saw, and here by the spread that was on top of the Cherubim like sapphire stone, the looks of the form of the Throne.”

In Talmud Yerushalmi it is implied that [tekhelet] is the color green, like grass.

All kinds of colors are auspicious signs for a dream, except for sky-blue [tekhelet].

Tekhelet - It is green. And someone who's face is green is sick.

Rabbi Yehoshua ben Korḥa said: Esther was called Hadassah because she was greenish, having a pale complexion like a myrtle, but a cord of Divine grace was strung around her, endowing her with a beautiful appearance.

What is the deepest ירק? Rebbi Eleazar said, like wax and like the flower of the qarmal tree; Symmachos says, like a peacock’s wings.

Esther was Yerakrokes, and a strand of kindness was drawn upon her. This means that her beauty and fairness had a glow that leaned toward the color Yarok. This glow made her exceedingly pleasant to the eye of one who saw her... and a glow like this is found in the precious stones known as Almas, which are very valuable because they are rare.

Observe [carefully] and make them like the pattern that will be shown to you on the mountain.

Come and see, when G-d commanded Moses regarding the Mishkan he could not comprehend it until G-d showed him everything in its form, each and every thing. How did [G-d] show him? With white fire, and black fire, and red fire, and green fire. What is written? "See and make them like the pattern that was shown to you on the mountain." Nevertheless, it was [still] difficult for Moses.

It boggles the mind - how was that generation, which had no craftspeople who were experts in this, able to build it?... Moshe Rabbeinu was not a craftsman nor was he actually shown the Mishkan and its accessories. Rather, as it says in Midrash, that HaKadosh Baruch Hu showed Moshe Rabbeinu a red fire and a white fire and a green fire and a Techeiles fire and then told him "make for me a sanctuary..." Moshe replied to HaKadosh Baruch Hu "Master of the world, from where shall I procure all of these fires?" [Hashem} Replied "See and make it like the pattern..." Meaning the Techeiles wool, dark red wool, crimson wool and fine twined linen. This is why the building of the Mishkan was written in the Torah and then repeated. Even though one could say, what matter does it make? What is done is done. But it teaches us a great lesson in the service of the Creator, how one can make themselves a vehicle for holiness...

...All of this was to illustrate to the children of Israel that just as they are able to translate the supernal sanctuary, with all of its combinations of Divine names, into this Mishkan which is made from inanimate materials - wood and stone and gold and silver and copper... How much more so is a human being able to make oneself a vehicle for holiness, to embed within oneself and within one's limbs all of the spiritual worlds and combinations of Divine names...