Regional Map - Lettering Problem

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Great maps, Valastyr

If this is PS and you still have layers, duplicate the parchment layer and raise it to just below the labels. Then create a mask from the labels and feather the mask outwards. Use the mask to create a layer mask on the new parchment layer, and what you should get as a result of that is a faint parchment halo around each letter that will give the illusion that the artwork below has been erased... whereas it in truth it remains untouched

That means you don't have any coloured halos that stand out from the rest of the map as being different.

EDIT: This is very much after about 4 more comments were added, but it just occurred to me that you could move your new parchment label outline layer down the stack till it was only just above the linework. Any colours you add would then also colour the new parchment layer, and the false erasing effect would only be on the linework.