Black marks on front of board from FCS fin installation..?

I recently had a custom board made and it has an FCS quad fin system install. The guy who shaped the board sent it to another guy to be glassed and to put the fins in. On the front of the board over where the fins were installed there are very obvious black marks that match the placement of the fins. I asked the shaper about it and this is his reply "That is how it's done, when you drill out the plugs for the fcs's, you have to go all the way until you touch the deck so when you put the resin in , it goes all the way and bonds to the deck for strength that's why you see the black rings because he used black resin. That's why you see on most boards the fcs stickers over the fin placements." Now at first glance this seems kind of weird because i haven't seen marks on a board like this. But i am uneducated on the process so i am wondering if this is a typical occurrence?