Why Are a Witch's Children Always Either Black- or White-Haired?

[On hiatus for now due to a lack of inspiration.] Tawada Hazuki seems like a wicked woman who runs a fortune-telling shop by day and an information brokerage behind the scenes. In truth, she's a witch from a village in another world, and her shop has a door that leads to different worlds. With her long lifespan, she thought she'd live out her days alone. Then she took in a human child, and before long, she couldn't stop taking on apprentices. The Akutagawa siblings from the slums, the white tiger from the orphanage, fine, but why are a psychic and a curse user being sent to her home too? The strangest thing is that the children in Miss Witch's home have either black or white hair. Is that the witch's unique type? "Haha, of course not! It's just that the children with talent happen to have black or white hair." "Hello? I'm about to die." The former Yokohama Mafia executive calls to harass her. Only the computer screen casts a faint glow in the dim room. The woman holds her phone in one hand and strokes the white-haired man in her arms with the other. "Pay off what you owe me first, then we'll talk." The call ends. "Miss Tsuki." The white-haired man who had been curled up in her arms gets to his feet. At around 190 centimeters tall, he pouts like a sulky puppy. "Will, we've got a big job." At that, the man flashes an eager, triumphant grin. "But first, let's pick up the kids from school." The witch may claim she doesn't like taking human disciples, but her home keeps filling up with human children. "Ryunosuke! Stop fighting with Atsushi. Gin, talk some sense into them!" "And Maboroshi, you used magic on that TV show last time, didn't you?" "Don't sneak around taking pictures on your phone, Jack. You're in trouble too!" The adopted children and disciples stand in the corner with their heads bowed, apologizing to Mr. Will. The moment Miss Witch appears, though, they happily crowd around her again. Will, Miss Tsuki's one and only: Damn brats... Tawada Hazuki: It's all right, Will is my favorite puppy. "We're family." The rookie author Oda Sakunosuke wins a prestigious award, the Heavenly Restriction tyrant enjoys a happy family and kicks the Zenin clan to the curb, the curse user and the Six Eyes strike the first blow against the jujutsu higher-ups, the gigantic Black Organization is crushed by a coalition of righteous groups... Behind all of it is that woman, pulling strings in secret, all to earn money to raise her children. "Long live money." The black-haired information broker and her experimental subject, an immortal hound, raise their glasses in celebration. My darling puppy, be reborn from the dust. Blood or bone, the wind will fan the dancing flames. The witch of dust keeps an immortal hound beneath the moonlit sky. Offer a kiss of true love to the dark phantom, and the world will see the light again. Note: An original black-and-white-haired pairing: a mature, money-loving information broker and an experimental subject, a white-haired wolfhound. The witch and immortal hound are both nonhuman. Theme: Giving children a warm home