I have a problem with the concept of making one white wrap in the first and last chulya. This effectively causes the one to fall short of making the 7 (or 13) completely blue chulyot. I find this problem since the Zohar (Shelah 172) seems to only mention blue chulyot with no mention at all of white wrappings.
1. The Gemara (Men. 38) is quite clear that that at least the first and last kerikha (if not hulya) is white.
2. Therefore, the Zohar cannot mean that all the kerikhot of tsitsit are blue to the exclusion of any white kerikhot.
3. The Rambam explains in Mishne Torah that the whole mitsvah of tekhelet is to make the wraps, and therefore calls the gedil “tekhelet”; nevertheless, he too says that the first and last kerikha must be white. Similarly Rav (Men. 39a,
see esp. Rashi, s.v. tekhelet).
4. Since only a single kerikha of an entire hulya is white, the hulya’s color would be considered blue (i.e., blue being the majority).
5. The concept of a white kericha/ot in tsitsit may be found in the Gra on Raya Mehemna (Pinchas 228b, mahadura batra), and Ramak on Shelah (175b). Note that according to the Remak the color of the kerikhot should have been white; the reason for leaving the beginning and end of the gedil white may be for the sake of “revealing” what is “hidden”, thereby alluding to the fact that the tekhelet is really just a “cover” and not the intrinsic color.
6. Although I personally believe that the intent of the Zohar and the Arizal is that all the kerikhot should be blue except for the first and last, the Sefer HaKaneh says to wrap alternate hulyot of white and blue (ending with white).
– Shlomoh Taitelbaum