Playing devil’s advocate, the GR”A was against Techeiles without a Mesorah.
Why is the word L’Dorosom inserted there and not the end of the pasuk? The pasuk almost seems to imply that the mitzvah
of Tzitzis will be L’Dorosam but maybe not the mitzvah of Techailes.
This proof is attributed to the Vilna Gaon (quoted in (שו”ת בית הלוי מהדורת אור החיים תשס”ז ח”ד ליקוטים סי’ ל