The basics of crossing a brown layer and a blue layer produce shades of green layers upon a few conditions being met.
First, understand how green is made. Blue shells are produced by bile being thrown back into the shell gland calcium so the actual shell is blue. (Crack open a blue egg and you will find blue inside as well). Brown eggs are produced by hemoglobin wash being applied to the shell (white from the calcite shell gland) so that it literally is "paint" applied to the shell. Open a brown shell and you will see white shell inside. Green is achieved by applying brown wash to a blue shell, so you need the genetics for both brown layer wash (about 13 control how much) and genetics for blue shell (2 genes involved with only 1 needed to produce blue color).
How deep a color of green (spring to olive) depends on how much brown wash is applied. For true olive eggers you need a dark brown layer line such as Welsummer, Marans, or Penedesenca. A middle brown layer line such as Barred Rock produces middle greens, typically, when bred over a blue line.
I can't tell from Hoover Hatchery if the Prairie Bluebell is truly a breed (meaning traits consistently passed along to offspring) or a hybrid (a mix of breeds creating a mix of trait results). They use the word "breed," but I suspicion in their description that it may be a hybrid since the lineage states Araucana and White Leghorn and the chick photos vary a lot. That could mean that your blue layer only has 1 blue shell gene to pass along. Why? Araucana are pure breeds for blue while White Leghorn have no blue genes.
To have this make more sense you need to understand some genetics. Every gene "slot" that controls a characteristic (trait) has 2 spots filled by 2 genes. One from the father. One from the mother. To consistently pass along a trait, a parent should have 2 genes thereby assuring that ONE of them will always be passed along to the offspring (generally matching with the other gene pair from the other parent keeping the line "pure").
With hybrids, you may only have 1 of the gene pairs for a certain trait. If the trait is dominant, 1 gene is enough to express that trait. If the trait is not dominant, but recessive, it takes 2 genes to express that trait.
With blue shells, it only takes 1 of the oocyan genes to throw bile back into the egg shell duct to create the characteristic blue shell. However, if you have a hybrid, it will pass that 1 gene 50% of the time meaning 50% of the offspring receive the blue shell gene while 50% of the offspring do not. That changes results.
If the Prairie Bluebells have been carefully controlled by Hoover to have 2 blue genes, then paired with a Barred Rock rooster (I presume), you will get 100% greenish layers that have 1 blue gene that is dominant for blue color. That 1st generation offspring bred back to the Barred Rock rooster will produce 2nd generation 50% blue shell (green layers) and 50% brown layers.
If the Prairie Bluebells are simply hybrids with mixed chances of whether the hen has 1 blue shell gene, then your results will vary. If you breed a 1 blue shell gene to the Barred Rock, 50% will become green layers, 50% will be brown layers (missing any blue shell gene).
If the Prairie Bluebell is the rooster, and the Barred Rock the hen, the same chances remain the same for the passing of blue genes for green shells, however you will have sex linked chicks...barred males (white head dot) and non-barred females (no head dot). If the Barred Rock is the rooster (and he is pure), all chicks will be single barred (1 barring gene).
Hope that helps and makes sense.
LofMc
