I have seen Mason's quote about the seal a number of times, but I have never seen it referenced as to being on a flag. Also, as per Washington's orders of the flags matching the regimental facings from this time, Virginia is to have red flags since they have red facings. And there are also surviving VA militia flags from the 1812 to CW era, and all the examples of these I have seen are white. Virginia may have some blue flags, but that far from being a set rule for their colors.