Is it true that STINGRAY's Marina the Mermaid was modeled after Sylvia Anderson?

Yes, as were THUNDERBIRDS' Lady Penelope Creighton-Ward and FIREBALL XL5's Dr. Venus, who were also voiced by Sylvia. Though Sylvia had been providing vocal, script, and production support since the early days of Anderson's work, FIREBALL XL5 was the first Anderson series to feature her face on a puppet.

Interestingly, though the resemblence in the cases of Venus, Marina, and Lady Penelope is almost impossible to deny (moreso in the case of Lady P), both Gerry and Sylvia Anderson and the puppet artists continue to state that none of the puppets were modeled on real people. The common story is that the puppets were sculpted to bear a very rough resemblence to pop stars or other celebrities of the day. Gerry attributes much of the more recognizable resemblences to artists following their directions too exactly: "We'd say we wanted our lead to look like a cowboy-type--`you know, sort of like Maverick'--and suddenly [STINGRAY's] Troy Tempest looks exactly like James Garner," Gerry once said in an interview.

However, chief puppet artist Mary Turner admitted later--much to Sylvia's surprise, according to Sylvia's book YES, M'LADY--that Lady Penelope was indeed modeled after Sylvia. The resemblence between puppet and famous face became even more pronounced when the SCARLET puppets were introduced: One frequent SCARLET guest puppet (Dr. Giordello in "Spectrum Strikes Back"; Glengarry Castle caretaker Mr. Morton in "The Trap") looks remarkably like Robert Mitchum; it is accepted wisdom that Destiny Angel was sculpted to look like Ursula Andress; Captain Scarlet, while supposedly sculpted after Cary Grant, bears a closer resemblence to voice artist Francis Matthews; Captain Blue and Colonel White bear uncanny resemblences to their respective voice artists Ed Bishop and Donald Gray.