Rashi on Numbers 15:38/רש"י על במדבר ט״ו:ל״ח

1ועשו להם ציצת THAT THEY MAKE THEM A FRINGE — It is called צצית, because of the threads that hang down from it. Similar is, (Ezekiel 8:3) “and he caught me by the curls (ציצת) of my head’’. (The word denotes something twisted as threads or curls). — Another explanation is: it is called ציצת because of the command associated with it (v. 39) “and ye shall look at it”. Similar is, “looking (מציץ) from the lattice” (Song 2:9). (The word therefore denotes “something looked at”) (Sifrei Bamidbar 115).

2תכלת BLUE PURPLE — It is the blue dye of (obtained from) the blood of the Chilazon (a kind of shell-fish).