It took 10 long years to finish the novel but Sussman is reaping big pay-offs: outside of New Zealand the novel has been picked up in the United States, South Africa and Britain.
It's "incredible and surreal", she says, considering that for years she questioned whether she should give up her dream of writing and go back to medicine. Even now, having done a Master of Creative Writing at AUT, during which time she wrote another novel (Sentenced, which won the 2014 Kobo/NZ Author Publishing Prize), she can barely dare to call herself an author.
"That's those people over there who are articulate and well-read and I find it all a bit terrifying," says Sussman, whose natural warmth makes it easy to see her as both a doctor and a particularly empathetic writer. "It just still feels too new, I guess."
The novel spent a long time languishing in her bottom drawer but, as the years went by, she honed her craft writing short stories (winning the Graeme Lay Short Story Award in 2012), and revisiting the book occasionally to apply her newfound knowledge. After sending it to a literary competition, she heeded advice to rewrite the entire manuscript in the first person.
"I was very close to self-publishing it and at least being able to move on. But it was a story very dear to me so I didn't really just want to leave it."
The Steiners promise to keep in touch and send news of Miriam as she grows up, but as the years drag by, Celia, who becomes increasingly destitute in her homeland, never hears from them. Meanwhile, Miriam struggles to find happiness in her new life in England, and begins to yearn for her roots. Although it's a fictional story of a mother and daughter torn apart by circumstance, it also questions whether cross-cultural adoptions made famous by stars such as Angelina Jolie are really in the child's best interest.
"It's always been an interesting debate: if you offer a child a loving family but remove them from their culture, which is better?" says Sussman. "I once heard a plastic surgeon speak about the layers of skin: clothing, culture, family. I became intrigued that if you take one of those layers away, how would that affect identity? In a way they're a protective covering. Remove one and people are quite vulnerable."
Sussman says she was painfully aware that writing in the voices of two black characters might be construed as presumptuous or offensive. But she reconciled it by thinking that many authors write outside their own realm of experience. "You just have to try and be as authentic as you can."
The novel is certainly that, bursting with colourful details of life in South Africa and Norwich, where Miriam moves; in some of the book's more violent scenes, it also draws on Sussman's medical knowledge.
"It's quite a privilege you have as a doctor. You're taken right into people's lives when they're at their most vulnerable. It gives you an incredible look into people's characters but it's also something that you'd never want to abuse. So I'm very careful with my writing, it's never directly related."
It's not until Miriam sets foot on South African soil as an adult that her childhood memories come flooding back, an experience familiar to the author, too. "When I started to write I was blown away by how emotional I found the process and how little bits of my childhood I'd completely forgotten came back to me."
When she was young her father was the head of Heinemann Publishing South, so he'd always bring home new books for an eager young Sussman to read. Then there were the cocktail parties where guests of honour such as Wilbur Smith and Frank Muir would tell stories. After school, she did a BA in English Literature at the University of the Witwatersrand, but the death of her father from stomach cancer saw her change direction and pursue a career in medicine.
While at university, Sussman became part of a group of protesters known as non-rotators: white doctors who refused to work in all-white hospitals. She met her husband, also a doctor.
Ten years after moving to New Zealand, where she completed her medical degree and became a GP, the couple moved to Europe for a two-year stint in Norwich (where her husband furthered his surgical training), and a year in Edinburgh. "We were two carefree backpackers, arriving home with two children, prams and all the rest of it."
Writing was a long-held dream and a more flexible alternative to medicine, particularly with kids. She still keeps her hand in, as a director of the couple's Auckland-based charity, Arch (Auckland Charity Hospital), a service offering surgery to those who have fallen between the cracks in the public health system and can't afford private care.
But it's her 10-year labour of love that she's most proud of. Shifting Colours may not completely assuage her personal guilt over apartheid but it will be a success, she says, if it gets readers thinking.
"There's so much intolerance all over the world, it would be wonderful if we just stopped for a minute and thought about it."
Shifting Colours (Allison & Busby $26.99) is out now.
