Why, exactly, are colors on various laptops/computers so different?

This may seem like a completely stupid question, but I’m interested in more than a basic answer. If at all possible, I would like the science behind it. Is it just as simple as “settings”, or does it depend on something individual that varies at the time of manufacture?

If you bought two of the exact same computers – made at the same time, same place, same parts, same everything – and if the color had never been changed manually on either of them, would the screens still vary in how they displayed color? That’s what I’m trying to drive at. If so, why is this?

—Inspired by @Jeruba for her answer here