I'm attaching a photo of an RO68b (WD Curtis Match stamp). Scott describes it as green, in the a, b or c paper. This is clearly silk paper type (b), but there is no indication of this stamp printed in blue or any color variation.
I have looked at it from the possibility of being sun changed, but the dark color of the blue matches that of other match and medicine examples, and there is 0 sign of changeling. I find it interesting also that the perf tips on left have part image from the adjacent copy, and they are a match as well.
Anyone have any idea about a blue RO68b?