YA Novel where the main characters family have been replaced by impostors

Question

There's not much I remember about the book. I know it has a green cover, the hardback version anyway. The green is almost shiny with vertical lines, sort of like the matrix.

This could be way off, but the title might be two words, the first being "the" and I have no idea what the second one is. But I could be wrong on even that.

The general plot follows a young boy, not sure of the name. He lives in a small town. At some point in the book, he discovers that his whole family and his best friend aren't human. I'm not sure if they are aliens or robots or some kind of impostors. I do know there was some way for the protagonist to know the difference, like some kind of physical marking on them that gave them away. The marking was either found on the arms or the back of the neck, but I'm not positive. I think the protagonist's friend, despite being a non-human/enemy, helps him in some way after protagonist finds out.

The story had a kind of small town/I'm alone in the universe sort of feel to it, if you get what I mean.

This is driving me insane. I realize that's not a lot of information, and it vague at that, but if anyone can think of what I'm talking about, it would be greatly appreciated. I want to say it's from the early 2000s, maybe mid 2000s. I believe I read it toward the end of elementary school and during middle school, which would put the dates around 2006-2009, but I'm not sure when it was published. As a frame of reference, I think I was reading it around the time I was really into the Uglies series, Gregor the Overlander, and any other sci fi books like that.

Answer 1

It may be a bit of a stretch, but could it be Piers Anthony's Race Against Time? It involves a 20th century white boy accidentally scratching off the skin of his friend, showing that it's all brown underneath, and that there's some vast conspiracy that everyone but him is involved in. I want to say that his friend still helps him, but the majority of it is him corresponding with a penpal through coded letters (they do something like having the message be in every third letter) to escape and find more people like him.

Of course, the reveal isn't that the people around him aren't human, but that

The human race has become a homogenous brown due to the mixing of races here in the 24th century, and the protagonist, his pen pal, and a few others are genetic throwbacks to earlier races being preserved in a zoolike "natural environment".

One of his clues (which matches what you're saying above about skin markings):

Item: Some of his schoolmates had skin that could peel off, like furniture varnish. Underneath it was tan. John's skin would not peel; it became tan in summer but faded to a pale color in winter.