It’s genetics. I explained and it makes perfect sense lol. If you can’t make sense of genetics from my explanation i also posted a link. Feel free to do your own research but the link I posted explains very well I think.
I agree with all the egger names getting out of hand.
Sorry, but you may have to clarify if I'm missing something.
Your link is somebody saying to assume that all easter eggers carry at least one copy of white eggshell.
They also appear to be assuming that all "purebred" blue egg breeds will have 2 copies of the blue eggshell gene... which, though they're "supposed to", it isn't guaranteed.
There is new technology that can test if your bird carries a blue egg gene.
Up until fairly recently, you had to test hatch to figure that out.
It's also very difficult to remove brown coating once it's in the genetics.
These are issues that crop up fairly often.
That's why people have to say "x% chance of laying a tan egg" (or green)
Marans are common for olive eggers. But any "dark brown" egg producer can be used.
Brown eggs are white eggshells, with a brown coat painted on top.
F1 Olive eggers automatically have 1 copy of white.
Things can get messy with F2 (or F1b. Etc whatever number you put) as they can inherit the white shell, instead of blue.
If somebody wanted to create a breed that produced olive eggs, I'm sure they could. (It can't be called an "Olive Egger" though.)
With the new technology to test for the blue egg gene, they would no longer have to test hatch hundreds or thousands of times. It could take years off the work to create a breed.
There's already green egg breeds, so it can obviously be done (Shetland Hen, Silverrudd's Blue)