You are attempting a project that is near and dear to my heart. Egg color.
Interesting egg. Very pretty.
Without having the egg shells in my hand, I can only give some educated guesses as to how that was produced.
From my understanding of egg color genetics, though, I think your egg is still a white based shell with heavy bloom with perhaps a bit thinner/more porous shell that allows the bloom to show through, rather than a true pink shell. (Your photos show white still on the edge.)
Genetically, base shell is either white or blue. Shell color comes from the calcium the hen produces from her shell gland. If bile is thrown into the mix, the egg shell is blue. If no bile is thrown into the base, the shell is white. There are 2 genes that determine the bile production into the base shell. Blue is dominant, so if you've got a single gene blue (like an EE) typically you have a paler blue. Two blue genes typically give you the darker blues.
Further tinting happens down the egg tract if the genetics are present to add a brown wash (from hemoglobin) to the base shell....just like painting a wall. It takes about 13 genes to cover the genetics for how much brown wash is applied. The heavier the wash, the darker the tint...from ivory, tan, to very dark brown. Some tints are pinker than others. Brown wash is pretty elusive. I've purchased non-laying pullets from really dark lines that produced, to my disappointment, moderate colors.*Usually* the color tone from a dark layer bred to a lighter layer is a middle tone between...but not always. I have two daughters from a Barnevelder and Splash Marans (at 5 scale...who should have been a 7 scale). One lays a pretty terra cotta color (about a 5 scale) the other is a plain brown. (About 3 scale).
Bloom, the final phase, is added at the end as a protective coating to prevent egg spoilage. Bloom can also have some tint, and from my understanding, it can be pink or a bit grey, which is how you can end up with mauve or lavender-ish eggs. The closest I've come to mauve is with a hen that laid heavier bloom over a pink-brown wash (lighter tint) applied to a base white shell. (That was actually a Black Sex Link of all things).
Whether to use a brown layer or a blue layer with that elusive bloom to produce pink or mauve, well therein is the question.
Color genetics dictate that brown wash applied over base blue shell produces green. The tone and color of green depends upon how much brown wash is applied. The darker layers such as Welsummer, Barnevelder and Marans lay a lot of brown wash over the blue shell which is how to produce olive eggs...breeding a dark layer over a blue layer. (My Barnevelder over my Cream Legbars produced daughters that lay a lovely olive).
Then we have to go back to that bloom, to which I've not seen any definitive genetics for. If tinted bloom is laid over a green egg or olive, you can get some interesting tones, depending upon what kind of green base you are working with. If it is more of a blue tone, you might end up with more lavender.
Historically, Langshan have supposedly been the answer to the mauve egg. (One line claims a Langshan line that lays mauve eggs...more of a "plum" than purple). They lay white base shells with brown tint and bloom.
Langshan traditionally were darker layers, and were used to produce the Marans lines. However, a lot of that dark wash has been bred out of Langshans as the breed fell into disrepair or was converted to more production. (Brown wash actually requires more time in the egg duct, so the darker layers are not typically your most productive layers.)
It is thought the Langshan lines create a pink/mauve coloring likely from the kind of bloom they apply over their brown tinted eggs.
So my best guess would be it is your Langshan, and that particular bird is laying somewhat thinner or more porous white shells with just the right touch of brown wash and bloom to produce a pink tone you can also see from the inside.
I would trap nest your Langshans first to determine if that is true.
I would also test the egg to make sure it is still strong quality (as why breed poorer egg shells...pretty color, but fragile eggs that will result in poor hatchability).
My thoughts. Keep us posted. I'd love to see your progress.
LofMc
PS: BTW I've gone more olive at moment...I had a set back with a coon that cleaned me out of Cream Legbars and my best Marans, so I'm currently in grow outs waiting to see egg colors arrive and further breeding potentials.
But I have produced some lovely olive and some really gorgeous terra cotta. But I do not currently have any birds adding enough bloom to produce a pink on my way to mauve. For that I'll have to play with my lighter tinted shells and was planning on getting some Langshans.
Good luck with your project

LofMc