In Spectrum Strikes Back (1967) it is mentioned that the only thing that can kill a Mysteron agent is high voltage electricity and that Spectrum has made an anti-Mysteron gun. However in both previous and following episodes we see normal guns with bullets killing Mysteron agents. Plus the Mysteron Gun does not appear in any other episodes except this one.
The type of powers the Mysterons have and what they can and can't do change through out the series. One example they take control of several vehicles with their powers without destroying them first, yet they don't bother using that particular power to take control of spectrum's vehicles when Spectrum try and stop them. Whilst this probably makes sense storytelling wise e.g. to stop the Mysterons from appearing too overpowered and winning the war all the time. It does raise the question of the limits of their powers.
Lieutenant Green is Colonel White's Executive Officer. It is questionable why he holds the rank of Lieutenant considering that this makes him junior in rank to the other Spectrum agents who hold the rank of Captain. Considering the seniority of his position he should hold the rank of Major or Lieutenant- Colonel.
In Operation Time (1967) it is first revealed that X-rays cannot penetrate Mysteron agents yet in the earlier episode Winged Assassin (1967) (the episode set straight after the events of the introductory episode), Doctor Fawn says he has been running tests on Captain Scarlet and we see X-rays in the background. Surely as part of his tests on Scarlet, Doctor Fawn would have seen that Scarlet is now impervious to X-rays.