patur– ”The Gemara in Shabbos (75a) says that according to Rabbi Yehuda, one who extracts the dye from the chilazon on shabbos is chayev for Dosh. Now the minimum shiur to be chayev for Dosh is a Grogeres. The amount of dye taken from a Murex Trunculus is less than a Grogeres.”
Now do me a favor, before you make it appear so simple, look into it. There is a machlokes rambam and raavad if dash needs the shiur grogros( shabbos 8:7 in yad) but if you would look in the kesef mishnah you would see that they are only arguing by oichel and everything else they agree on that even less than a grogros is chayav. V`ayin od bchasam sofer shabos 75a dh hatzad that has a pshitus there has less than a grogros in each chilazon.