There are lot of research papers on egg color in chickens. If you want to learn how it all works I can send you a couple of references.
Basically the blue egg gene is dominant. A hen only needs to get the blue gene from one parent to lay blue eggs. The blue egg gene produces a blue shell.
All of the brown egg genes are a coating that goes on the out side of th shell. Brown and Blue make green. The more brown the darker the shade of green.
White X White = White
White X Blue = Blue
Blue X Blue = Blue
Blue X Light Brown = Green
Blue X Dark Brown = Olive
Note: To get the "bluest" eggs you oviously have to work with a Blue X Blue. Look at the inside of the shell of the blue eggs. Some will be pale or white on the inside. the darker blue on the inside the better blue gene is going to be expresses in offspring. Also..if you are getting green eggs it mean that you have some brown egg genes in the line. You will have to select you breeders for the eggs with the least amount of green.
I am interested to know if it matters which parent has the blue gene. say brown gene father and blue gene mother, white gene father and blue gene mother. Can the blue gene be passed through the mother or only through the father? Does that make sense?
I am not sure about the blue eggs. I have a study on blue eggs that I haven't read yet. I will let you know if it says anything about that.
I have heard that in the Marans that the Dark Egg color is more influenced by the father than the mother (although I haven't seen any study to confirm this). The father may have a larger influence on the blue egg color too.
There is an interesting article that discusses color inhibiting genes--genes that sit around the blue or brown color gene and suppress or decrease the degree that the color is expressed so a blue may be more pale or brighter blue depending on if the chicken carried one of these color inhibiting genes.
Here is a link that discusses the color inhibiting genes: http://marans.org/eggreview.pdf It also has some pretty detailed information regarding egg colors in general.
In a nutshell, both blue and brown pigments are governed by dominant genes. If a chicken lacks both of these genes, it will lay a white-shelled egg. A chicken will inherit one copy of each gene from each parent for a total of 2 genes. If the hen lays blue eggs she must have at least one copy of the blue gene and maybe two. If a rooster comes from blue-egg laying parents he will also (most probably) carry the blue gene--then off you go!
The bogie outlier is if one of the chickens carries one of these color inhibiting genes. Basically, cross the deepest blue layers, wait for the chicks to lay and only breed the deepest blue layers.