While there is no prohibition on wearing blue dye from another source, the rabbis maintain that other kinds of "tekhelet" do not fulfill the mitzvah of "tekhelet", and thus all the strings have been traditionally kept un-dyed (i. e., white) for many centuries. In recent times, with the (debated) re-discovery of the Ḥillazon in the "Murex trunculus" mollusk, some have noted that one cannot fulfill the mitzvah of "tzitzit" without the "tekhelet" strand. This position, however, has been strongly disputed. Others have disputed whether the coloring that comes from the "Murex trunculus" is the same as the biblical "tekhelet", based on the fact that according to traditional Jewish sources "tekhelet" is supposed to be a dark shade of blue, while wool that was discovered in archaeological excavations and was found to have been colored with Murex dye is violet.