"You shall make the robe of the ephod all of blue.
Exodus 28:31
Surrounding context
28:30 And you shall put in the breastplate of judgment the Urim and the Thummim, and they shall be over Aaron's heart when he goes in before the LORD. So Aaron shall bear the judgment of the children of Israel over his heart before the LORD continually.
28:31 "You shall make the robe of the ephod all of blue.
28:32 There shall be an opening for his head in the middle of it; it shall have a woven binding all around its opening, like the opening in a coat of mail, so that it does not tear.