I use my mon mono only when I travel and the last time I got on a plane, I noticed that the back strap was a wholly different color from the other vachetta (the whole strap). It’s weird bc I usually wear mine with my initials on the inside as much as it is on the outside- so it can’t be the exposure. Any clues as to what this is and any quick fixes? I even tried putting mink oil on that back strap twice to no avail. Front (last pic) and back photos for reference. TIA!