Jothar you say there are serious questions on the murex.
Bring them on!
You say “how can the Jews have lost a process that their neighbors next door were still using?” see Codex Justinianus see 4:40:1 in which the Roman empire banned purpura dye to laymen at the same period in which tcheiles was lost to the jews (bet. Rabanan Savorai and early Geonim).
You say “the latest archaeological evidence shows a darker techeiles color than what is being use” see Radvaz(??? ??”?)that the strength of the dye isn’t ????. Besides, what dose one peice of cloth found whith blue murex dye have to do with the halachic requirements of tcheiles?
You say “The dye from murex trunculus changes color depending on exposure to sun. It can have many shades.” True as the Tosfos Hashalem (?’ ???? ?”? ????? ????) brings a midrash that says that different dyes are made from the chilazon, however chazal say the color of tcheiles is indistinguishable from kala ilan, thus we know it’s exact color. The shade however is not ???? as I wrote above.