Picture of Jews in a Bais HaKneses wearing Talleisim with Techeiles.
This manuscript of the Tur was written (as per is colophon) in Mantua Italy 1435. It is now owned by the Vatican. The picture, depicting a synagogue scene, was drawn as a hakdamah to Tur Orach Chayim. The tichales is most clearly shown on the chulyos of the man holding the sefer torah. He has 13 chulyos alternating white and blue (as per Baal Ha’Itur). Here is a link (http://digi.vatlib.it/view/MSS_Ross.555).
The “money picture” is 12V.
Not that this proves Jews were actually wearing Techeiles at that exact time (though they might have), but it shows that Techeiles always was traditionally “blue.” When Rashi writes “Yarok,” (yellow-green) or Rambam writes “Shachor” (black), or the Romans referring to it as “purple,” it might refer to their cultural understanding of the same color which we today identify as “blue.”