No, I think you're right: it didn't get its last layer.
I have Cuckoo Maran hen that lays nice dark eggs (not dark like a Welsummer egg, but much darker than my Golden Sex Link's terra cotta colored egg). BUT it's clear that the last, darkest layer of color is applied just before the egg is laid, because it can be scratched off with a thumbnail. The moss in the nest often sticks to the wet egg, and when you pull the moss off, it takes the color with it.
Once we got a nearly-white egg from that same hen with a twisted, pinched narrow end. It had a goopy blob of colored...stuff...stuck at the pinched end. (I know it was the same hen, because we only have 3 hens, and had gotten a white and a terra cotta egg from the other two, that same day.) So, the color was clearly mis-applied to that egg somehow.
I have also gotten some 'dusty' looking eggs from that same hen. I'm convinced it's something wrong with her internal color-sprayer.
But this would also explain perhaps how she lays dark eggs with darker speckles - that's where the color is applied in extra layers.