I interpret the flat layer as a normal paint layer, otherwise @mdfm28 would surely have named it more precisely. With any luck, he might be able to join this discussion and tell us more about the function of his Cheap Ballpoint pen Brush.
However, his statement is not that this white outline has to happen, but that it could happen and seems more like a possible unwanted side effect if you read his text carefully:
Michelist
Hello @AhabGreybeard! 