About the test being that ???? ??? ??? ????, ????”? ??”? ??. ???? ???”? ?”? ????, ??? ???”? ??????? (????????, ??? ?’ ???? 333) ??”? ??”? (???? ?????”?) ??”? ??:)] all clearly say that kla ilan is indigo and the test does not work we are obviiously doing the test wrong which means the test is lo maaleh vlo morid.
However, I did hear from one of those osek in this inyan that they did the test on some old kla ilan and it got lighter and the way they extract the kla ilan today is different. See also the above post from HOlymoe
Now regarding your original point about the dye deteriorating I will quote you from the ”tekhelet” site
“We performed an experiment, wherein groups of snails were killed on
15 minute intervals, the being extracted dye after death. Thus we had samples of dye extracted from snails that had been dead for 15min, 30min, 45min, etc.. The results showed that the greater the elapsed time the more severely the dye was reduced until the dye was no longer viable. This was explained physiologically based on the fact that the dyestuff from the Murex is composed of two components extant in the gland – (1) the dye precursors, (2) the dye enzyme (purpurase). The enzyme acts on the precursors upon exposure to oxygen (i.e., when the gland is squeezed). The purpurase, however, deteriorates in a short amount of time subsequent to the death of the snail. So, if one tried to squeeze the gland after the snail was dead, the purpurase
would no longer exist to act upon the dye precursors.”
The gemara is not a contradiction at all. The time when you are chayav for netilas neshama according to the GEMARA 107B (and see the rambam 11,1 in Hilchos Shabbos) is when you make the animal a goses not when it dies. ??”? ????? ???? ???? ??? ???? ??????