The stain is smooth like the rest of the surface. Using alcohol wipes doesn’t seems to remove. It looks like u put a magnet on the fridge and after sometime u remove it, there is a stain, like outside the magnet area has aged more.It may not be a stain at all, it may be from a part of the case rubbing against the MacBook.
When running your finger over the "stained" area, do it feel any different than other areas of the top case?
It’s not abrasion, cause the magnet is hidden inside the fabric.If it's caused by abrasion, it's permanent. Next time put it in the pouch with the flap to the bottom of the case.
Or get a pouch designed to protect the device, not damage it.
It could be from abrasion because the inside of the carrying case is probably smooth and could have been rubbing against the MacBook like very fine sandpaper. I often use fine grain sand paper to get a smooth finish on wood and plaster.The stain is smooth like the rest of the surface. Using alcohol wipes doesn’t seems to remove. It looks like u put a magnet on the fridge and after sometime u remove it, there is a stain, like outside the magnet area has aged more.