Meiko "Menma" Honma from Anohana: The Flower We Saw That Day. The symbolism works both ways, as after dying as a child, she has grown, but her demeamor remains the same, so she's a ghost but also innocent.
The eponymous Index has silvery-white hair, a Photographic Memory, magical abilities, plus information from over 103,000 grimoires hardwired onto her brain. The setting takes place in a city dedicated to the study of people with Psychic Powers (the training programme for which is actually a disguised magical ritual) called espers.
Also by CLAMP, in Clover, Suu has white hair and is the most powerful magical being in that world.
Dragon Ball Super reveals Goku's latest and by far most powerful form: Ultra Instinct. In its completed form, it turns Goku's hair a shining, whitish silver. It allows him to master a technique even the Gods struggle with. What the transformation is and what exactly caused it is unknown, but its certainly different to the usual Super Saiyan transformations
Fairy Tail has Mirajane, Elfman, and Lisanna Strauss, sibling wizards.
The Children of Befort from Fantastic Children are not like anyone around them, and their white hair shows it.
In Full Metal Panic!, Teletha "Tessa" Testarossa and her Aloof Big Brother Leonard both have white hair; both are among the Whispered, children born during a supernatural event which has given them uncanny knowledge of futuristic technological advancements and some low-level Psychic Powers.
Goblin Slayer shows dark elves. These are very similar to the drow, and have dark skin as well as white hair.
The .hack franchise has Aura, a young girl with long, flowing white hair and robes. She's also the Ultimate AI who serves as the "guardian" of The World.
Etienne of Innocents Shounen Juujigun has stunning white hair and "powers" as a blessing from God, including lightning bolts from the sky, healing the sick, bringing the dead back to life, causing an eclipse, and having supernatural luck that makes him almost impossible to kill.
All dog-demons have silver hair and golden eyes when in their human forms, as seen with Sesshoumaru and both of his parents. His younger brother, the titular Inuyasha, is only half-demon. He shares the silver hair and golden eyes of his father's family but, during every new moon, his hair becomes black and his eyes brown. This symbolises the loss of his demonic powers, forcing him to spend the night as a full human.
Bat-demons have dark skin and silver hair, as seen with Tsukuyomaru and his father. Unlike most of his race, Tsukuyomaru liked humans and fell in love with one, much to his family's shame. His daughter, Shiori, has inherited her father's dark skin and silver hair. She was bullied and ostracised by the human village she was raised in because her appearance signified her demonic heritage.
Kanna is one of Naraku's creations and serves him. She has jet black eyes and silver hair, and is regarded as strange and mystical by everyone. This is because she is the essence of the Void; her powers are connected to mirrors and the soul, she doesn't display any emotions and she barely speaks. Even Naraku's other creations don't quite know what to make of her.
Towa Higurashi from the sequel Yashahime: Princess Half-Demon, one of Sesshomaru's daughters, also has white hair, like her father and her half-uncle.
The half-demon Raita also has white hair. This is one of his non-human marks.
Anna and Neko (pinkish-white), who are Strains, people who receive powers not from a King, (though they do both become Clansmen of Kings).
Adolf K. Weismann, the Silver King, though he had this before he was chosen as a king. Though he's only evil when he's possessed.
Yashiro Isana, the protagonist or, to be more precise, Tooru Hieda, who he was body-swapped with. White Hair, Black Heart also applies here when he's possessed by the same body snatcher, and Sukuna Gojo, a Green Clansman, who don't really have any born connection to the series' powers.
And finally, the Green King's hair changes from black to white when he unleashes his power in Season 2.
Both Tomoe and Mizuki from Kamisama Kiss have white hair but look like they're in their late teens to early twenties. Neither is human; Tomoe is a Kitsune and Mizuki is a Divine Beast.
Several characters including the protagonist have white hair in Kiznaiver. This is a sign that they participated in a failed experiment when young, and their hair turned white prematurely.
In Kurohime the titular character is a white haired gunslinging witch.
Ginko's white hair and single green eye are a result of being entangled with a certain kind of mushi. It's later revealed the mushi that affected him was called "Ginko", which he took as a name after it took all his memories of his life before. It was the only name he remembered at the time.
In Nanatsu No Taizai, the Goddess Clan's royal bloodline have silver-white hair... when their faces are visible at all. Usually they're obscured by magical light (maybe holy power bleaches?). Most 'mere' Goddesses have blond hair. This trope is also an indication that the Liones family adopted its youngest child, since she looks so different from them. The usual symbolism of a special destiny and strong magical talent also applies.
Naruto: Members of the original Otsutsuki clan, who came from a world outside Earth, all have white hair (bluish white in the anime). A few of their descendants, such as Kimimaro of the Kaguya clan, inherit this trait.
Leticia too. She is a vampire with blonde hair so light that they have also been described as being "shining blond-silvery". Other people can recognize that she is a pureblood vampire simply because she has "hair so beautiful that no human could possibly have".
The original Queen Serenity. Sailor Moon herself was originally supposed to be white haired when transformed and blonde as Usagi. This was vetoed by Naoko Takeuchi's editor Osa-P. In the manga, she does have white hair as Princess Serenity and Neo Queen Serenity, but not in eitheranime.
Technically, Yaten/Sailor Star Healer has silver hair.
Sailor Cosmos has white hair in two heart shaped odangos and pigtails that reach her feet. It's unknown (other than that she's the true form of Chibi Chibi) just what she is, or what relation she has to Sailor Moon and it seems the mangaka intended it that way.
Usagi was apparently suppose to have white hair in general (since Minako, the original Sailor heroine, was already a blond) but the author's editor told her to make the main character blond since that would be better received by the targeted female audience.
Rally Cheyenne from Silent Möbius is half-Lucifer Hawk (demon, basically), and her silver hair marks her as having some of the strongest magic in the series.
An interesting variation occurs in the Slayers series: protagonist Lina has reddish colored hair, but when she casts a particular high-level spell, her hair turns white. This occurs once in the Light Novel series, and twice in the anime.
Kantarou from Manga/Tactics has albinism, which is a mark of his unusual spiritual gifts as an onmyoji.
Played with in Tokyo ESP, in that the origin of Rinka's white hair is different depending on the medium. In the manga, she always had blonde hair that was so light it would look, to the casual observer, like she had white hair. In the anime, Rinka is actually a brunette whose white hair manifested when she gained the power to phase through objects.
Tsukiuta's Shun, the "White Demon King", an Idol Singer with actual magic powers. The truth is, he's in a sort of yin-yang connection with Hajime, the "Black King" and leader of the unit that's Shun's unit's rivals. Both are just as mystical, but Shun is the one who flaunts his powers, while Hajime is still in denial that he even has them.
Yumi from Ulysses 31 belongs to a race of blue skinned, white haired human looking aliens called the Zotrians. The Zotrians are also known for their exceptional beauty.
Redhead Masane Amaha from Witchblade becomes this after she becomes corrupted with her battle suit.
In X1999, Princess Hinoto has white hair and is one of the most powerful magical beings in that world.
Kisara of Yu-Gi-Oh!, the Mysterious Waif with connections to the Blue-Eyes White Dragon. Unfortunately, her white hair and pale skin led to discrimination and loathing by the people of ancient Egypt.