On a recent "American" board , made in China, so no warning legends of PbF . Don't know what its called, the sort of conformal coating final process at the pcb production phase is a staining coat , usually green these days. White rings showing around the solder pads after soldering may show elevated soldering temperature has been used or wrong composite material body , showing rings of plain white polyester+fibre board . The green staining having melded into the plastic or evaporated.
From UL 6 digit E number and board type this is designated 260 deg C / 10 second solder dwell ( for conventional soldering) rather than 270 deg / 10 second dwell of proper made for PbF pcb boards.