The stamp, unveiled by President Francois Hollande on Sunday's national day, shows the face of a youthful, dewy-eyed Marianne from the shoulders up, her long hair flowing down and her hand raised.
"For all those who ask who the model was for Marianne, it's a mix of several women, but particularly Inna Shevchenko," Olivier Ciappa, one of the stamp's designers, said on his Twitter account.
The 23-year-old Shevchenko, a Ukrainian who has been granted political asylum in France, is the leader of the French branch of Femen, a self-declared "radical feminist" group known for its topless protests against sexual exploitation of women, sexism and religious institutions.
Speaking on Monday after his Twitter comment caused a stir among France's conservatives - with the right-wing Christian Democratic Party calling for a boycott of the new stamp - Ciappa reiterated that the Marianne portrait was inspired by "a mix of real people".
Aside from Shevchenko, he also pointed to actress Marion Cotillard and Justice Minister Christiane Taubira as sources of inspiration for the stamp, which was co-designed by artist David Kawena.
"For me, Marianne, who is represented bare-breasted, would probably have been a Femen in 1789 (the French revolution) because she fought for the Republic's values - liberty, equality and fraternity," Ciappa said.
"Inna is the only one among those who inspired me who is not French."
Among critics, the "French Spring", a grouping of gay marriage opponents, hit out at what it called the "new Marianne".
"Are there not enough beautiful and emblematic women in France that we have to import our models from Ukraine?" it lamented on Twitter.
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