Jason for sure does not care what happens to kaneki's hair. It should also have been a bit mroe gradual, as he was down there for 10 days, so Jason probably saw it in the intermediate stages. Rather, in the anime there is 1 instance, and in the manga, 2.
The beginning of the second season, Touka comments that he needs a wig if he is to return to Anteku due to its color.
In the Manga, Touka does the same thing in chapter 79. The second instance comes much later when Kaneki meets his favorite author. He is pretending to be human at the time, and she comments on his hair, Prompting Kaneki to reply that it is white Naturally. This happened in chapter 108/109.
Its never really been the focus though. Rather, Ishida uses his hair as more of a symbol of his mental state and its changes. As it changes colors, so too does he. If he had not included people commenting about it, Fans would have made elaborate theories on how only we could see it changing and try to reason it.