Let me try this with symbols. A capital "O" represents the dominant blue egg gene. A smaller case "o" represents the not-blue gene. Since blue is dominant if just one of the genes at that gene pair is blue the hen will lay a "base blue egg. What I mean by base blue is that all eggs are either base blue or base not-blue. I call it not-blue because that specific gene does not color the eggshell, just allows the default white from the materials that makeup the eggshell to show. It defaults to white if the blue gene is not present.
There are several different gene pairs that can affect brown. That's why you can get so many different shades of brown, from tinted to the chocolate brown from Marans or others. Some are dominant, some recessive. Some partially dominant or only act if another specific gene is present. One bleaches out brown. One is even sex-linked, the pullet can get it from her father but not her mother. It can be complicated and you don't always get what you expect.
Brown is generally laid on after the eggshell is formed, though of course there has to be an exception to make it more complicated. There is one gene that can cause "tinting" throughout the eggshell. The Blue gene colors the eggshell all the way through, not just on the surface like Brown.
For your purposes with the olive eggs, the brown will be laid on during the last half hour or so the egg is in the shell gland after the rest of the eggshell has formed. Green is simply brown on top of blue. It goes like this.
Base Blue + no Brown = Blue
Base Blue + Brown = Green
Base White + no Brown = White
Base White + Brown = Brown
Your Marans is pure for not-Blue. That means he has o,o at that gene pair. Your EE might be pure for Blue (O,O) or might be split for Blue (O,o). You cannot tell by looking at her eggshells. If she is pure then all of her offspring with that Marans rooster will be O,o and lay a base blue egg.
If she is split then their offspring could be either O,o or o,o. This does not mean that if you hatch two pullets one will lay a base blue egg and one will not. The odds of each pullet laying base blue are 50-50. It is very possible you will get both base blue or neither base blue. If you hatch a lot of pullets then your odds of half of them laying base blue increase but you have to have enough pullets for the odds to mean something. You might look up Punnett Squares to see how to calculate the odds of the crosses.
The brown genetics works the same way but there are so many different genes that have an effect that it can get really complicated fast. Sometimes you get real surprises with the eggs, especially a couple of generations into the breeding project where recessives have a chance to match up.
The way I'd approach it would be to only hatch eggs that are base blue. And I'd look to hatch the darkest eggs since that seems to be your goal. You can pair an offspring with a specific parent to enhance certain genetics, like using that rooster over his daughters to set more dark egg genetics. That does not mean the eggs will get darker, it does not mean you won't get some lighter eggs. That just depends on how the various genes go together. But your odds of continuing to get dark eggs is much better.
The way I understand your goals I would use a rooster that hatched out of a dark green egg within a couple of seasons. Since a rooster doesn't lay eggs you don't know if he inherited the blue egg gene or not though NatJ's comments on comb type might help with improving your odds with that. If you are consistent with only saving breeding chickens from your dark olive eggs you can increase your odds of having pullets that lay base blue eggs.
I did this with my base blue hens and base not-blue rooster and got very lucky. The rooster I kept had a blue egg gene. Within a couple of generations practically all of my pullets were laying blue eggs. With the lottery that is genetics it could have easily taken several more generations to get to that point.
Good luck and have fun with it.
There are several different gene pairs that can affect brown. That's why you can get so many different shades of brown, from tinted to the chocolate brown from Marans or others. Some are dominant, some recessive. Some partially dominant or only act if another specific gene is present. One bleaches out brown. One is even sex-linked, the pullet can get it from her father but not her mother. It can be complicated and you don't always get what you expect.
Brown is generally laid on after the eggshell is formed, though of course there has to be an exception to make it more complicated. There is one gene that can cause "tinting" throughout the eggshell. The Blue gene colors the eggshell all the way through, not just on the surface like Brown.
For your purposes with the olive eggs, the brown will be laid on during the last half hour or so the egg is in the shell gland after the rest of the eggshell has formed. Green is simply brown on top of blue. It goes like this.
Base Blue + no Brown = Blue
Base Blue + Brown = Green
Base White + no Brown = White
Base White + Brown = Brown
Your Marans is pure for not-Blue. That means he has o,o at that gene pair. Your EE might be pure for Blue (O,O) or might be split for Blue (O,o). You cannot tell by looking at her eggshells. If she is pure then all of her offspring with that Marans rooster will be O,o and lay a base blue egg.
If she is split then their offspring could be either O,o or o,o. This does not mean that if you hatch two pullets one will lay a base blue egg and one will not. The odds of each pullet laying base blue are 50-50. It is very possible you will get both base blue or neither base blue. If you hatch a lot of pullets then your odds of half of them laying base blue increase but you have to have enough pullets for the odds to mean something. You might look up Punnett Squares to see how to calculate the odds of the crosses.
The brown genetics works the same way but there are so many different genes that have an effect that it can get really complicated fast. Sometimes you get real surprises with the eggs, especially a couple of generations into the breeding project where recessives have a chance to match up.
The way I'd approach it would be to only hatch eggs that are base blue. And I'd look to hatch the darkest eggs since that seems to be your goal. You can pair an offspring with a specific parent to enhance certain genetics, like using that rooster over his daughters to set more dark egg genetics. That does not mean the eggs will get darker, it does not mean you won't get some lighter eggs. That just depends on how the various genes go together. But your odds of continuing to get dark eggs is much better.
The way I understand your goals I would use a rooster that hatched out of a dark green egg within a couple of seasons. Since a rooster doesn't lay eggs you don't know if he inherited the blue egg gene or not though NatJ's comments on comb type might help with improving your odds with that. If you are consistent with only saving breeding chickens from your dark olive eggs you can increase your odds of having pullets that lay base blue eggs.
I did this with my base blue hens and base not-blue rooster and got very lucky. The rooster I kept had a blue egg gene. Within a couple of generations practically all of my pullets were laying blue eggs. With the lottery that is genetics it could have easily taken several more generations to get to that point.
Good luck and have fun with it.
