For the record, I just realized default colors of iemguis is note "pure white" as we've been discussing.
Sure it is "witheish", more precisely, it is "FCFCFC" instead of "FFFFFF" (pure white). So a very light grey color (99% brightness in the grey scale). This is not a regression, it's the same in pd 0.48, which I also tested.
I don't know why or where that happens in the code
cheers