The bestselling American author Rick Riordan has thanked his Russian publisher for no longer “whitewashing” its jacket illustration of his character Carter, an African American boy who has been depicted as white on the covers of various foreign language editions of Riordan’s young adult series.

Riordan’s Kane Chronicles cover the adventures of siblings Carter and Sadie Kane, who are descended from the magicians of Ancient Egypt. Carter’s skin is “dark brown”, like his Egyptologist father, he tells readers in the first pages of The Red Pyramid. His sister Sadie’s is much lighter, as she takes after their mother, who was white. “Carter, you’re getting older. You’re an African American man. People will judge you more harshly, and so you must always look impeccable,” his father tells him.

‘Fixed’ ... one of the new Russian covers for the Kane Chronicles.

Despite this, Riordan’s foreign publishers in countries including Russia, Italy and the Netherlands have featured cover images of Carter as a white boy. “Pretty art but I’m not amused how they whitewash Carter,” wrote Riordan of the Italian jacket last year.

This July, he provided a link to the Dutch edition of The Serpent’s Shadow, saying that “the whitewashing of Carter Kane continues … Ugh. Like almost all authors, I have no control over covers and the publishers do not ask for my input,” wrote Riordan at the time. “I don’t even see the covers until they are published. But I have made my displeasure known. (It’s not just the Dutch, btw.) I’m sorry: ‘People in our country will only buy books with white people on the cover’ is not a valid excuse.”

The Dutch publisher subsequently listened to Riordan’s concerns, the author said, and revised the covers “so that Carter Kane actually looks African American rather than whitewashed”.

His Russian publisher has now followed suit, prompting Riordan to write last week: “Thank you to my Russian publisher EKSMO for listening to my concerns. They have fixed the Kane Chronicles covers so Carter is no longer whitewashed. This art will be featured on any future reprints.”

The news was welcomed by campaigners for diversity at We Need Diverse Books. “We’re glad to see an author with as broad an audience as Rick Riordan fighting for accurate representation on his covers,” said spokesperson Lamar Giles. Riordan, whose books include the bestselling Percy Jackson series, is regularly named one of the world’s richest authors by Forbes, last year making $13m (£8.5m), according to the magazine.

‘No valid excuse’ ... one of the original ‘whitewashed’ Russian covers for the Kane Chronicles.

Nancy Gallt, Riordan’s US literary agent, said that while his foreign contract requires translations to be “faithful and accurate”, the agency and its authors “have virtually no creative control over the book covers – even in the US, much less the 40 or so other countries where Rick’s books are published”.

“With the exception of the US and UK, we don’t even see the covers until they are published, and even with these Rick only has input, not control. Many foreign editions use either the US or the UK cover, but an equal number have original designs which we do not see until the sample editions come in,” she said.

“We assume the publishers are operating in good faith, but if there is a problem with the covers, we bring it up with the publisher, as we did with Russia. We’ve had no part in ‘whitewashing’ and we’ve never condoned or failed to object as soon as we’re aware of it.”

Riordan’s Dutch publisher told the Guardian that its original cover featuring Carter Kane as a white boy was a regretted error, rather than an “issue of whitewashing”.

“It has unfortunately been a regrettable omission in the cover briefing for the designer (who is in absolutely no way to blame for what happened). In the original cover art briefing for the first book, emphasis was placed on creating an exciting image that would be in line with the previously published Percy Jackson books,” said editor Suzanne Verkoren of the Dutch Riordan jackets. “This has resulted in the depiction of Carter Kane as looking similar to Percy Jackson. This should never have happened and the Boekerij editors regret it.”

Following Riordan’s tweet about the situation, the publisher contacted his agent to explain what had happened, and the covers were then adjusted.

But despite the changes made for Riordan, Alexandra Strick, manager and co-founder of Inclusive Minds, which campaigns for diversity in children’s books, said the issue of “whitewashing” was “still a very major problem in children’s books”.

“There is a very strong sense that black characters have been – and continue to be – left off book covers. The problem is widespread,” she said. “There have been many high-profile cases of characters actually changing colour completely, so described in the story as black but then appearing Caucasian on the cover. However, very often it’s more subtle than that, with the cover of a book about a non-white character often avoiding featuring a human face at all, or with the character featured in silhouette or even with their face turned away. Sometimes it’s a case of publishers asking that a character is ‘less dark’ almost as though mixed race is acceptable but somehow black skin isn’t.”

In 2009, the author Justine Larbalestier battled her American publisher to have the jacket of her novel Liar accurately reflect its black protagonist, after early copies featured a white girl. Her publisher, Bloomsbury, apologised, saying that it regretted that the “original creative direction for Liar – which was intended to symbolically reflect the narrator’s complex psychological makeup – has been interpreted by some as a calculated decision to mask the character’s ethnicity”.

Ursula Le Guin, whose classic stories of Earthsea feature the wizard Ged, who has “red-brown” skin, has been outspoken about the issue. Blasting the Sci Fi Channel for its almost entirely white adaptation of Earthsea in 2004, she wrote in Slate that she has also had “endless trouble with cover art”. Ged, who has red-brown skin because “I didn’t see why everybody in heroic fantasy had to be white”, was a “pallid, droopy, lily-like guy” on the first British edition.

“I screamed at sight of him,” wrote Le Guin. “Gradually I got a little more clout, a little more say-so about covers. And very, very, very gradually publishers may be beginning to lose their blind fear of putting a non-white face on the cover of a book. ‘Hurts sales, hurts sales’ is the mantra. Yeah, so? On my books, Ged with a white face is a lie, a betrayal – a betrayal of the book, and of the potential reader.”

More than 10 years later, Strick said that “in terms of whether this is changing, there is a slight sense that things are improving a little in terms of awareness within the industry, but I would say less so in terms of end products. Books continue to seem strangely cautious, finding ways to avoid the issue or compromise.”

She pointed to “a ridiculous (perhaps self-perpetuating) myth that a book with a black character (or indeed a disabled character or a female character) on the front cover, will be perceived as being ‘for’ that particular ‘minority’ audience as opposed to for general readership”.

“In our work, we also still often get told that ‘diverse’ books are seen as ‘niche’ books, which simply has to change. Diversity means all of us,” she said. And as Inclusive Minds relaunches its #EverybodyIn campaign for diversity, Strick called on “all” of us “to play a part in demanding that the book world find stories about characters of all backgrounds and include them on the front cover”.