Basically you have your seat, and your seat bottom (cushion). There are two peices of the fabric, one that goes over the back of the seat (we call it the "seatback") and one that goes over the cushion ("seat bottom"). When one gets gum on it and/or puked on and/or spilled on and/or stained etc in any way that's noticeable, usually the groomers will see that as they are grooming the aircraft, and pull the fabric off (attaches via velcro strips) and go find a new one and slide in on. However, it could be a case similar to our Hawkers where different aircraft may have the same seats but a different colour fabric. When this happens we do our best to match the colour, but sometimes it just doesn't work out that way, and we have to steal one from the bin for another aircraft, and use that untill we find one the proper colour for that aircraft.
Way to go, nice and slow, never late, 748!