If today we no longer have the techelet, which was used to paint one of the threads of Tzitzit, with the color techelet, Sky blue, Since nowadays we have no more traces of this chilazon , can this tzitzis wire can be painted with other types of Paints? What halakha says about that, is it about people who wear tzitzis painted blue?
The mitzva is specifically to color the string with the blood of the chilazon fish. Painting it blue is not enough, and the tzitzis are indeed posul. This is why nowadays, and for the past hundreds of years, Jews have not been coloring some of the strings blue. Over the years many people have attempted to identify exactly which fish the chilazon is, specifically in order to be able to paint the string with the correct dye. Otherwise, if it isn’t the correct thing, we don’t just paint the string blue.
Rambam HIilchos Tzitzis 2-1,