User blog comment:BriceBlueGuy Wiki/Lincoln's White Hair Theory/@comment-31753089-20171122222037

I agree with you. A lot of people think he inherited it from Pop-Pop, but it makes no sense: Lincoln said several times he doesn't know why his hair is white, he would have known it if he simply inherited it, right? Chris Savino said he isn't an albino, also because he would have had pale skin and red eyes. We saw only three people, including him, in the show which are fully white-haired so this color isn't surely natural in the show, as in reality, and I don't think his hair is white because he is stressed, he had it since he was very young, when he wasn't stressed, or at least not the way he is now:  https://vignette.wikia.nocookie.net/theloudhouse/images/b/b1/S2E07B_Young_Lori_feeding_young_Linc_ice_cream.png/revision/latest/scale-to-width-down/320?cb=20170227201501

So poliosis is the only plausible explanation, in my opinion, even if it would be a particular kind of poliosis, since it usually causes one or multiple white patches on the hair, and not all white hair.