I was asked about the suitability of coloured threads in a
Tallit (not Techelet, but specifically colours to match the colours of the
materials used in the Mishkan).
There is a clear prohibition in the Talmud against using an ‘indigo’
dye.
If you are using kosher Techelet, that’s fine, but you can’t
use anything that could be confused with the colour of Techelet.
There are statements in Halacha that the threads, other than
Techelet, should be white. Rambam says that and even the Ravad – who famously disagrees
with Rambam about almost everything only disagrees about how much Techelet should
be used, and agrees that the rest of the threads should be white.
However there is a clear instruction, again, in the Talmud that
“the threads should be like the garment.” That’s clearly understood to mean
that if you have a woolen garment you need woolen Tzitzit etc. i.e. the thing
that needs to agree is the MATERIAL. But the Shulchan Arukh says that “some
people understand that the COLOUR of the threads has to match the COLOUR of the
garment. That was news for me.
The Shulchan Arukh is a Sefardi legal authority and the
leading Ashkenazi authority, the Rema, writing right on that comment in the Shulchan
Arukh says this;
והאשכנזים אין נוהגים לעשות הציציות רק לבנים אף בבגדים
צבועים ואין לשנות
Ashkenazim only make Tziitzit with white [threads] even on
coloured garments and this should not be altered.
The Mishneh Brurah, also Ashkenaz, has no problem with a
coloured garment, but suggests that ‘careful’ people should use white since
that is definitely OK and also matches a verse in Daniel (the book, not the
father!) that describes God’s clothes as white as snow - ולבושיה כתלג
The Bach (the legal authority not the composer) and the
Magen Avraham also make a point about white threads matching God’s white
garment.
So …
It’s not ideal.
There is a possibility of relying on it, according to the
Sephardi Shulchan Arukh.
There is certainly fulsome support for a coloured garment,
and also a nice idea about white threads.
But on the basis that the Shulchan Arukh notes that some say
the threads on a coloured garment should be coloured, it’s definitely not
forbidden.
I’ve put all the sources referred to in this document
https://www.sefaria.org/sheets/625023?editor=1