Billing Displacement: We'll let Chris Bentley explain this one (from The Complete Gerry Anderson: The Authorised Episode Guide):
Although voice artist Lian Shin is credited on 20 episodes of the series, ("The Launching") features her only vocal appearance as Harmony Angel and she does not portray any other characters. For all of Harmony's previous speaking roles, her voice was provided by Liz Morgan... Harmony is seen in a number of later episodes, but this is the last time that she speaks.
Defictionalization: Both catchphrases of the show have been borrowed by American private spaceflight firm SpaceX to describe its readiness for rocket launches, modified to "SpaceX Is Green" or "SpaceX Is Red".
Name's the Same: It is rumoured that music group The Spectrum's involvement came about more or less accidentally; Gerry Anderson was made aware that their name and the SPECTRUM organisation's name might cause a trademark conflict. Rather than pick a new name or call the lawyers in, he chose to Take a Third Option and offered them the title-theme gig.
The Other Darrin: Harmony Angel is voiced by Liz Morgan except for "The Launching", where she's voiced by Lian-Shin.
Referenced By: The show's Smash Cut style was Amusingly played with by Chris Evans in TFI Friday, where he would try to flip his head between two cameras in time with the Captain Scarlet riff.