Speak unto the children of Israel, and bid them that they make them throughout their generations fringes in the corners of their garments, and that they put with the fringe of each corner a thread of blue. NUMBERS (15:38)

TALLITS - FOR PRAYER
NO LONGER HAVE THE BLUE BECAUSE THE FORMULA WAS LOST.
OR MAYBE THE DESCENDANTS OF CONVERTS CAN'T WEAR BLUE TZIT-TZITS?