Is there a reason for the black stripes on the Tallis Gadol or Katan, or is it just purely design?
The black stripes are for the beauty of the mitzvah and to commemorate the mitzvah of techeles. See also: https://asktherav.com/19432-19447-is-there-an-issue-with-having-a-black-tallis-gadol/ Sources: ראה בכ״ז: לקט יושר הל׳ ציצית…