Exodus 12:13

12:13 The blood will be a sign for you on the houses where you are, so that when I see the blood I will pass over you, and this plague will not fall on you to destroy you when I attack the land of Egypt.

Exodus 26:4

26:4 You are to make loops of blue material along the edge of the end curtain in one set, and in the same way you are to make loops in the outer edge of the end curtain in the second set.