Everybody loves Michelle Obama. That’s not my opinion, it is a fact. I know this because I have been reading her memoir, Becoming, and every time I take it out of my bag, someone tells me how much they love her – my hairdresser, who put his scissors down to stroke the glossy cover reverently, a lady next to me on the tube, almost everyone on Instagram. Two teenage girls in Starbucks, who were waiting for their toffee nut latte frappuccinos, waved at me, pointed to the book and made love-heart shapes with their hands.

As a result, you would have a better chance of catching a glimpse of Father Christmas when he comes to town this December than Michelle Obama. Tickets to her talk at the Royal Festival Hall in London sold out in moments, and she has cosy couples’ dinners with friends including the Clooneys and the Duke and Duchess of Sussex to squeeze in while she’s in the UK. And yet, you can’t miss her. Her image is everywhere. It has been two years since the end of Barack Obama’s presidency, and this is the second coming of Michelle. She is no longer a plus one. This time around, the first lady comes first.

Michelle Obama at the Royal Festival Hall in London. Photograph: Yui Mok/PA

And this new Michelle Obama looks different. Gone are the Gap-holiday-advert rainbow-bright colours, the neat pencil skirts and cute gingham checks, the school-fair-cake-stall J Crew cardigans. Instead, she is luminous and serene in all white, refined and elegant in wide trousers and silky tailoring. On stage on Monday evening, she looked positively angelic in a long white jumpsuit.

For her portrait on the cover of Becoming, in which she writes of having learned that “optics governed more or less everything in the political world”, she has chosen neither the cocktail dress you would expect of a first lady’s memoir, nor the trouser suit that might hint at a run for office. Instead, she wears a white T-shirt that falls completely off one shoulder, so that she seems to be wrapped in white drapery rather than dressed. Obama is a Grace as painted by Botticelli, rather than a politician on a podium.

“When they go low, we go high” is perhaps Michelle Obama’s most famous quote. If politics and culture seem to have sunk pretty low of late, the symbolism of all-white – transparency, optimism, peace – signals resistance. “Since Barack left office, I have read news stories that turn my stomach,” she writes of the Trump era in Becoming’s epilogue, but “what I won’t allow myself to do is become cynical”. It was in off-the-shoulder white, again, that she launched her book tour in Chicago on a stage with Oprah Winfrey, wearing a wide-necked blouse frosted with pearlised sequins and high-waisted trousers. In the UK and US editions of Elle this month, she wears a crisp white dress under a black leather Dior corset belt. For TV appearances, she has worn lots of white (a Rachel Comey wrap dress, for instance) and trousers more often than skirts (a pinstripe Jonathan Simkhai two-piece is just one of her recent trouser suit outings). Meredith Koop, who has been Obama’s stylist since 2010, told the New York Times that she and her client were steering clear of fitted dresses on the book tour, so as to make a distinction in the public mind between Obama now and her time as first lady.

Anne-Marie Curtis, the editor-in-chief of Elle UK, met Obama in New York in September. “She was wearing a cream trouser suit and very high stilettos. She is extremely tall and incredibly toned, so she is seriously imposing. For her portraits in Elle, we wanted images that felt like fashion, but also a true portrait of her. There is a candour to wearing white that connects to the book, and how honest she is.”

Many first ladies have achieved style-icon status, but what separated Obama’s tenure from those who went before her was the ability to project the sense that a real person was occupying the White House. “Diana did something similar in bringing a tactile, human warmth of tone to the British royal family,” says Curtis. “You know that thing where you meet someone and you immediately want to please them? Michelle has that. It’s very powerful, that kind of charisma. She’s warm, but you also get the impression that she wouldn’t suffer fools gladly. She makes you want to be a better person.”

Michelle Obama visiting pupils at the Elizabeth Garrett Anderson school in north London. Photograph: Jack Taylor/Getty Images

In Becoming, Obama comes across as steely and soft in equal measure. She praises Valerie Jarrett, for whom she worked at City Hall in Chicago, as being “both tremendously confident and tremendously human”. She is devoted to her husband, but never dazzled by him – some of the best bits of the book are when she calls him out for classic thoughtless-husband moves, such as the presumption of his going to the gym on the way home from the office when she had delayed young Malia and Sasha’s bedtime so that they could see him. (“I could be supportive, but I couldn’t be a robot,” is how she came to define her own way of being a president’s wife.)

But what makes Obama powerful as a style icon is not her designer wardrobe, the definition of her upper arms or her keen eye for colour. It is that she doesn’t really care about clothes all that much. It is striking that in the chapter about her wedding, she reminisces about the pastor, the music (Stevie Wonder) and the giddy buzz of exchanging vows, but doesn’t mention her dress. She gets misty eyed about a dress only once in Becoming: the white Jason Wu gown she wore for the 2009 inauguration, which, at the end of a long and exhausting day, “performed a potent little miracle, making me feel soft and beautiful and open again, just as I began to think I had nothing of myself left to show. The dress resurrected the dreaminess of my family’s metamorphosis.”

Most of the time, her engagement with fashion combines the uncomplicated joy of dressing up for a rare date night with a savvy understanding that taking charge of optics is a non-negotiable part of public life, but it does not dominate her life. “I think she likes fashion as much as the next woman – which is to say quite a lot, but not obsessively,” says Curtis.

Grace is a word Obama uses a lot. “If there was a presumed grace assigned to my white predecessors, I knew it wasn’t likely to be the same for me,” she writes of being the first black first lady. “My grace would need to be earned.” Grace is a virtue and a code of honour, but it is also an aesthetic, one which Obama and Koop utilised in a culture war. “I was female, black and strong, which to certain people … translated only as ‘angry’,” she writes. She earned that grace. She is not in the White House any more, but there is a lot of love in whatever room she is in. And that is a beautiful sight.