1. the test on kla ilan and techailes is actually a raya to the murux. Because if the gemara says you need a chemical test pashtus that means it was a different color or it means all the tanaim and amaroim were color blind. NOw the chiluk between kla ilan and the murex that if you put them in bleach the klah ilan will loose its color quickly, while the murex after a few months will still not loose its color. The gemara says the chemicaL test will make the kla ilan loose its color.
2. About it being nignaz, this was said by R yose and ameimar ( close to 300-400 years later) had techailes. So go figure.