There is a moment just before Chimamanda Adichie nips back to her hotel room to grab some lipstick when she turns and checks with our photographer: "You know how to light dark skin?" It is a throwaway question, and follows their discussion about camera lenses preferring matt over glossy lips (which hog the flash), but it encapsulates how life, for Adichie, is dominated by the simple matter of skin tone: her dark, Nigerian skin tone.
Or, to be precise, life outside Nigeria, where the 35-year-old writer grew up before moving to America, aged 19, and "became black".
She laughs, putting on a fake surprised voice, "Oooh! I'm black!" Then adds: "In Nigeria, I never thought of myself as black, because I didn't need to."
In Nigeria, she also never had to grapple with the fact that for black women, what Western magazines call "nude" underwear is anything but; nor did she get wound up by editorials claiming that "pink lipstick is universal": the reality, as her latest protagonist, Ifemelu, puts it, is she'd "look like a golliwog if I tried that shade of pink".
Such talk, such blatant language, should have me, the sort of well-meaning white liberal she parodies in her new book Americanah, squirming in my seat. After all, as Adichie says: "Race is very uncomfortable."
But after spending five years writing a novel that puts race under a "gritty" spotlight, this is a conversation she wants us to have. Adichie says it barely took any time for America to make her aware that her skin colour, "gingerbread" – a colour she "actually, really, loves" – comes replete with "baggage and assumptions in certain societies". This much she learnt early on.
"When I was an undergraduate, I wrote an essay for the first day of my English class, and it was the best essay in class. My professor walked in and said, 'Who's Adichie?' – Americans would sometimes tell me that from my name they assumed I was Italian – so when I raised my hand, I saw on his face this expression of surprise. That's when I realised, 'Oh! The person who wrote this essay is not supposed to look like me.' That was when I understood why race is a stupid, absurd thing. That you look a certain way, and people have all sorts of assumptions, right?"
Adichie rips those assumptions apart in her typically compelling third novel, which is a love story at heart, one that centres on a Nigerian girl who left her homeland to study in the US.
If that sounds familiar, then yes, a laughing Adichie admits: "Ifemelu is a more interesting version of me. A lot of her experiences are mine but not all of them.
"I like to think of this book as having a cinéma vérité quality. I didn't want to write a lyrical, Proustian book about race. I wanted to write a gritty, taken-from-real-life book."
And yes, Adichie's hair is every bit as "Afro kinky" fabulous as you might expect given Ifemelu's obsession with the stuff. Indeed, hair is practically the book's third protagonist after Ifemelu and her high-school sweetheart Obinze.
For Adichie, it's political: her hairstyle is a statement against the idea that "beauty has become this homogenous thing". That's why neither she nor Ifemelu straightens their hair, preferring an Afro or the cornrows with extensions she is sporting for her trip to London.
Arriving in America all those years ago, Adichie gained another new identity: "I became African, as well. In Nigeria, I didn't think of myself as African. But in America, everybody wanted me to tell them about A-fri-cah! I'm thinking, 'I don't know anything about Kenya.'" Again, that laugh: "I'm from Nigeria."
Not that she expects people to know much about her home country: "When people tell me they've been to Nigeria, my question is, 'Why?' I think Nigeria terrifies people, which is a shame. But we don't really try to make you like us. It's the big man syndrome. 'We're big and we have oil.' Of course, I think Lagos is the real Africa."
I interject: I'm nervous to use the "A" word, I tell her, ever anxious in my white liberal way not to insult. "I don't like that at all!!" she squeals. "Oh Lord. This is wrong. I want to have a conversation. Please. Please!" The problem is, most of the time people just don't listen. "There's this determination that Africa has to be a place that requires my charity somehow, so I don't care what you're saying," she says, paraphrasing the classic do-gooder.
Take the lady who approached her after a recent reading in Oslo: "She said she really wanted to help," Adichie smiles, "'Nigerians with computer skills'. I said, 'Yeah, but people have phones. I text my uncle who's in my ancestral hometown.' But she just kept telling me about how she wanted to 'help Nigerians with computer skills'. And I thought, 'This woman has what she has in her head and it doesn't matter what the reality is.'
"I'm thinking, 'Why don't you help, by finding out the policies your government has, and see how you can petition to change certain things that bring about inequality, rather than going off to 'help starving Africans'?'"
Today, Adichie, who is playing up her heritage in a stunning dress that her Lagos tailor made from local fabric, says she has "one foot in Nigeria and one in America", where she lives in Maryland with her doctor husband, but stresses that the Nigerian foot is the "more solid". She is back and forth between the two countries and says she could absolutely envisage winding up in Lagos one day.
For now though, she "likes being able to leave".
She owes her considerable fame – her second book, Half of a Yellow Sun, was a best-seller, winning the Orange Prize, and nearly four million people have watched her TED (Technology, Entertainment, and Design) talk on national identity – to a fellow countryman, the great Chinua Achebe, who died last month.
He gave her 10-year-old self, who'd grown up on a diet of Enid Blyton – thinking books had to have English characters – the confidence that people like her, a girl of Igbo descent, could exist in novels.
I'm struck by hearing Adichie, the fifth out of six children, grew up in a house that Achebe once lived in. Talk about destiny! But she says the significance was lost on her until she published her first novel.
"My editor said, 'WHAT?' And I thought, 'Oh, my God, yeah! That's actually kind of weird, isn't it? Now it's a point of pride. I'm like 'YES! Chinua Achebe's literary spirits were left behind for me!'" (Her parents, James, who was a professor of statistics at the University of Nigeria, and Grace, who became its first female registrar, inherited the house on the Nsukka campus from Achebe, who also taught there.)
This is a big year for Adichie, who will see her "baby" – Half of a Yellow Sun – make its cinematic debut this autumn in a film starring Thandie Newton and Chiwetel Ejiofor. It's slightly odd to hear her rave about Newton, a friend, playing the part of the Igbo Olanna, given that seconds earlier Adichie was decrying the fact that "the black people who are stars in Hollywood are all light-skinned" and saying she gets "very, very" frustrated that black women are so marginalised on the big screen.
"There's no dark-skinned woman who is a babe. There just isn't. The dark-skinned woman, she is the Serious One. She is the Friend. She is the Sassy Girl. She is never the person we root for." (That said, the London-born, bi-racial Newton is British, and the film is largely Nigerian-financied.)
Nigerians are in uproar about the decision, which had nothing to do with Adichie, to cast Newton. "They're like 'Ohhhhhhh!'" she admits, but brushes aside their qualms that Newton doesn't look Igbo: "My brother is lighter than she is." She is sympathetic about Nigerians wanting a local actress but says film-making is about "who's good, who has been tested, who can do it well". I want to add: "And who's marketable," but I bite my tongue.
If it seems churlish to finish back where I started by focusing on race, well, Adichie wouldn't have it any other way. As she puts it: "Just being aware is really important. It's also wonderful that the world is so diverse. I don't want everybody to be the same. I would be bored to death."
1977 Born in Enugu, Nigeria. Her father, James Nwoye Adichie, was a maths professor and later vice-chancellor of the University of Nigeria. Her mother, Grace Ifeoma was its first female registrar.
1995 Studies medicine and pharmacy at the same university.
1996 Leaves for America.
1997 Published Decisions, a poetry collection.
2001 Graduates from Eastern Connecticut State University in communications and political science.
2002 Shortlisted for the Caine Prize for "You in America".
2003 Completed an MA in creative writing at Johns Hopkins University, Baltimore. Her first novel, Purple Hibiscus, was published. It won a Commonwealth Writers' Prize.
2006 Her second novel, Half of a Yellow Sun, was released. The story about the Biafran war won the Orange Prize for Fiction.
2008 Received a MacArthur grant of $500,000 which allows her to write full time. Also completed an MA in African studies at Yale.
2009 A collection of short stories, The Things Around Your Neck, released.
2013 Publishes Americanah.