Make unexplored areas of a map shimmer when the map is held in hand

Some areas on a map are very similar in color to the parchment texture that's used for unexplored areas when the map is held in hand. This makes it very difficult to fully explore a level 4/4 map. It becomes obvious that you missed a spot when you put it in an item frame, because the missing parts are a different color there. If the unexplored area was animated or changed color, like with the enchanted shimmer effect, it would be easier to tell the difference between unexplored areas and explored areas that have blocks with a similar color as the parchment texture. It would also make sense, lore wise, because the map fills itself out, so it's obviously magic.