I personally think this makes them look “cool” — think racing stripes on sports cars — and these stripes beautify the practice of wearing the prayer garment and enhance the prayer service. But I asked a great Rabbi in Jerusalem and he told me a different and better explanation.
The Torah states to put strings on four-cornered garments that we wear, and one of the strings is supposed to be “techelet”. Techelet is sky-blue wool. It is dyed with a special dye made from the blood of a fish/snail called the chilazon.
Over the centuries, the exact identity of the chilazon became forgotten. Hence, the “string of techelet” became a mitzvah we are unable to fulfill (according to most authorities).
The idea behind the tzitzit strings is that they serve as a reminder. Like royal subjects who wear special insignias to symbolize their loyalty to the king, we wear tzitzit to remind us of our duty to God. The beautiful blue reminds us of the sky, which in turn inspires us to ponder God’s greatness. Now that we no longer have techelet, we have the stripe on the prayer shawl to remind us of the techelet.
Some people have a blue stripe, and many others have black stripes. According to some authorities, the prayer shawl should be the same color as the strings — white. Each person should follow his family and communal custom.
