I read this book, when I was young, about a kid getting trapped in an alternate universe. The alternate universe was a mirror image of the real world, but in black and white. The kid remained in colour, and I vaguely recall the colour being a crucial part to getting back home.
In the real world, there was some sort of catastrophe, where a group of children all went missing. It turns out they were trapped in the black and white dimension, but had been trapped for so long that they also lost colour.
I remember there was some sort of twist, but I can not remember what that twist was. I remember that one of the trapped kids managed to escape, but it was not who the main character suspected it to be; I do not think that was the 'big' twist, because I recall that in the last moments, the good ending went sour.
The book would have been around in the mid 90s, and it was in English. I am sure I borrowed it from a library, I'm Australia, should that mean anything. I was only a kid, when I read it, but I do not want to discount books you would not expect a kid to be reading; I was a bit more advanced than other kids of my age, in regards to reading and literature.