No basically since the plot has already been written, his effort to change the plot by changing hair colour is nullified. It will always keep reset again
This is pure sorcery now. Everything else in the BL could have been explained by our MC being over imaginative and "pure coincidences" but not this !?!
It’s a world where paranormal things like ghosts and people with psychic powers exists, besides there’s this weird phenomenon where female characters with little importance don’t have faces (literally). Having a hair dye being reset is not strange.
Girls don't have faces when they're in places where some other couple is stealing the spotlight. You'll notice our MC's face always gets cropped out of the frame when the scene is about his lil bro and Toujo and gang. But he appears fine to us when it's his pov. And remember his cousin's wedding where the cousin was blurry, thats because it wasn't her scene but I'm sure in private the cousin has a real personality and face otherwise how TF did husband fall in love with her.
Nope. Even the protagonist says so in the first 3 chapters he said that one factor that made him realize the type of world he is living in, is this weird thing where he can’t see women faces. He even said that he can tell who is a trap or a real women because the pretty girls that he can see the face are 100% trap. Well, there’s a lot more details on those chapters so it’s better for you to reread them.
Did he take a shower or something for his black hair to disappear?
If colour doesn't retain then try the same hair style!