Rebecca Hall was in her mid-20s when she first started to understand her complicated family history. The British actress-turned-director says most would look at her fair complexion and dark hair and see “English rose”, she says – but looks are never the end of a person’s story.

Hall, who has appeared in films including Vicky Cristina Barcelona, Frost/Nixon and Holmes & Watson, is the daughter of the late renowned British film and theatre director Peter Hall and the American opera singer Maria Ewing.

Her maternal grandfather, she learned, was a light-skinned black man who “passed” for white for the majority of his life.

It was about 13 years ago, when Hall picked up the 1929 novel Passing, by Nella Larsen, that she started to consider her own mixed-race heritage and why it had never really been spoken about in her family.

Set in the Harlem neighbourhood of New York, Larsen’s exploration of race and the practice of “passing”, which was not uncommon for light-skinned black people wanting to escape racial segregation and discrimination in that era, struck a nerve.

Finding out about her own history led to Hall adapting the novel for the big screen; the story follows two black women, Irene Redfield (Tessa Thompson) and Clare Kendry (Oscar nominee Ruth Negga), who could both “pass” as white but choose to live on opposite sides of the colour line.

“I think so many people are not aware that it happened because it’s a historical event that was necessarily hidden,” Hall tells Sky News.

“So a lot of families, it’s hidden even within those families, including my own. My grandfather was African-American and he passed white for most of his life. And that is a fact that I’ve only really fully learned details of in the last year or so.”

Before she read Larsen’s novel, Hall says she had no context or even any way of describing how her grandfather had lived his life, and why. “So it gave me an enormous amount of context and understanding and compassion and empathy for the choice.”

Passing tells the story of former childhood friends Clare and Irene, who are reunited one summer and Irene discovers Clare has been passing as white; she is even married to an overt racist (played by Alexander Skarsgård).

The film uses the notion of passing to explore not just racial identity but gender and the responsibilities of motherhood, sexuality and the performance of femininity.

It is not about critiquing those who chose to pass, says Hall, but about critiquing “a society that, in any way, judges a person’s construct of themselves… there’s the things we think we believe, the person we think we ought to be, that society wants us to be. And there’s the thing we really want to be, that we desire to be. And sometimes that can be a huge conflict zone, and it means sometimes that we’re hiding our true selves.”

Passing is Hall’s directorial debut and it has been many years in the making. “I faced problems both within the industry – I came up against blocks trying to get it made – but I also came up against personal blocks,” she says.

“[The screenplay] sat in a drawer for quite a long time because I just didn’t have the confidence. I felt like it was too ambitious… and I just didn’t believe anyone would let me make it.”

Hall feared that some in the industry would question her suitability for telling this story.

“The pitch meetings were particularly poignant,” she says. “I ended up getting very emotional every time I was pitching it to some financier because they would invariably ask me, you know, ‘why on earth are you making this?’

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“But I feel like I’m this sort of walking example of what this film’s all about. You know, everyone looks at me and has a whole set of assumptions that aren’t necessarily true. Or they’re true but it’s not the end of the story.

“Forever, everyone’s looked at me and known that I’m Peter Hall’s daughter and I’m part of a British theatrical lineage, and [I’m thought of as] ‘English rose’, and that’s sort of the end of the story. And the fact that within my own story there’s… so many other contradictory and elusive things sort of points out the absurdity of it all.”

Hall has shot the film in black and white, something she would not budge on. “In a very soundbitey kind of way, it just felt like the best way to make a movie about colourism was to take all the colour out of it,” she says.

“But I think more specifically what I mean by that is, I think sometimes to understand truths about humanity, we need poetry. We don’t necessarily need complete reality, sometimes the abstraction helps.

“I think black and white takes these concepts and sort of highlights that we’re so busy putting everyone into these categories, when no one can be reduced to a single thing. Like, you” – she gestures to me – “can’t be reduced to just ‘woman’ or, you know, ‘white’, or whatever it is… the great irony about black and white film is it’s not black and white, it’s grey. And this is existing in the grey areas, actually.”

Making the film opened up a lot of conversations between Hall and her mother that had previously been left unsaid.

“She’s extremely proud and she’s extremely emotional about it,” says Hall. “She said that she felt it had given her and her father who’s no longer with us a sort of release in a way, like an ability to talk about something that up until this point felt like it couldn’t be addressed.”

She adds: “I hope, sort of in the broadest sense, the thing that people take away [from the film] is, thinking about what the legacy of a life lived in hiding is. And that doesn’t just mean racial hiding, it means all the ways in which we’re not showing up for ourselves completely. And how we can’t because of how much society imposes something – especially black women.”

Passing is out now on Netflix