distribution of brown colour in the eggshell

You know how we we've always been told that the brown pigment in the eggshell was really pretty much all in the cuticle, and that that the calcareous part was really pretty much white? I always wondered about that; brown eggshells often look pretty brown on the inside, to me, even if the outside is somewhat darker (much darker, in the case of Marans and Welsummers and the like). The latest research results:

"Most previous studies have suggested that the bulk of the shell pigment is deposited in the cuticle of the shell. The present study measured the levels of protoporphyrin in intact eggshells and in shells from which the cuticle had been removed, using eggs from flocks at 3 different ages. This enabled the calculation of the relative amount of protoporphyrin in the calcareous eggshell and the cuticle layer of the eggshell. The majority of the protoporphyrin pigment was located in the calcareous part of the eggshell (80–87%) with a minority contained within the cuticle (13–20%)."
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I had a marans egg the other day with a huge brown splotch of dark on the round end, and lighter brown everywhere else. I also find I can scrub the brown off if I want, and if I get a wet, just laid egg, the brown comes off in my hands. The eggs in question are young pullet eggs.

Yeah, that's the part of the colour that's in the cuticle - Marans eggs seem to have the heaviest concentration in the cuticle, and it often comes off if touched when fresh-laid, or when washing, it seems. But they're still brown underneath, right?