Techeiles as a Light-Fast Dye

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Username: 613 mitzvot
Full Name: Yosef Malkiel
Posts: 6
Joined: Wed Feb 08, 2023 10:57 pm

Both Murex dye and indigo are incredibly light fast as natural dyes go.  Do we have a mesorah that techeiles was/had to be light fast at all? Rambam (Mishna Torah Tzitzis 2:1) says שעומדת ביפה ולא תשתנה, however Kesef Mishna says this is referring to the Gemara Menachos in which the Rabbis speak of the various tests to distinguish techeiles from kela ilan.

As far as I can tell, the Gemara is not discussing the light-fastness of techeiles dye.  Most natural dyes are generally not light fast.  Do we have any Jewish sources suggesting techeiles was light-fast or unusually light-fast?
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