“Techeilet” – turquoise, the beautiful color described in Menachot 43b as “resembling the sea, which resembles the sky that resembles HaShem’s Throne of Glory.”
The first mention there is in the Torah of “Techeilet” is in connection with the “Mishkan,” the portable Sanctuary that served as the Temple, the spiritual center of the Jewish People, until the erection of the Holy Temple in Jerusalem by King Solomon. The “Mishkan” served first in the Wilderness, and it was constructed of materials donated voluntarily by the Children of Israel; among them wool dyed the color of “Techeilet,” as we read (Shemot 25:3), “This is the donation that you should take from them… and turquoise, purple and scarlet wool…”
In the “Mishkan,” that wool was used in curtains, as we read, “You shall make the ‘Mishkan’ of ten curtains – twisted linen, with turquoise, purple and scarlet wool – with a woven design of Cheruvim you shall make them.” (Shemot 26:1), the Partition between the ‘Holy’ and the ‘Holy of Holies:’ “You shall make a Partition of turquoise, purple and scarlet wool, and linen; twisted; he shall make it with a woven design of Cheruvim.” (Shemot 26:31) Also a Screen for the Entrance of the “Mishkan,” “You shall make a Screen for the Entrance of the Tent, of turquoise, purple and scarlet wool, and twisted linen, the work of an embroiderer.” (Shemot 26:36) And all instances where beauty was required to enhance the House of G-d on earth.