The numbers are vinyl stickers made by the Television City Graphics department.
Before the new color scheme, the boxes received at least one other full makeover. In the early days of the game, the boxes were made of a thinner, lighter plastic-like material (I'm no engineer -- I don't know what it's called). Seemingly every time a contestant won and dropped the top half of the box on the floor, it would crack and need to be repaired or replaced. Eventually, the boxes were remade from a plastic that was slightly thicker, heavier, and sturdier. Although I still wouldn't recommend dropping them on a hard floor.
