Where does it say that John isn't blond? {John Dies at the End Series}

I remember, a while back, seeing some posts online about how people thought that John was blond, only for him not to be. I initially avoided reading these because I hadn't read all of the books yet and didn't want to be spoiled for anything. I just finished book #4 and I have found no description of John's hair color anywhere (since his eyes are blue, I assumed his hair would be blond).

Am I stupid or missing something?

The movie doesn't count. Though I haven't watched that yet, either.