Exodus 28:28

28:28 They are to tie the breastpiece by its rings to the rings of the ephod by blue cord, so that it may be above the waistband of the ephod, and so that the breastpiece will not be loose from the ephod.

Exodus 28:31

28:31 “You are to make the robe of the ephod completely blue.

Numbers 15:38

15:38 “Speak to the Israelites and tell them to make tassels for themselves on the corners of their garments throughout their generations, and put a blue thread on the tassel of the corners.