Pizza Stone turned black

When preparing pizza on your Grill Guru, always use a combination of a pizza stone and a Plate Setter with diffuser stones. You put the pizza stone on the grill grid. The grid is closer to the fire. It is therefore very likely that the temperature measured on the grid is much higher than the temperature indicated by the dome thermometer. A difference of, for example, 35 degrees Celsius is certainly not crazy. Keep a dome temperature of about 250 degrees Celsius.