It depends on your overall goals. If you can, keep both roosters to ensure the greatest potential for color. If you can't, then decide if you want to work for olive or eventually blue-green in the line with the one rooster....or always keep a pure breed breeding flock and work only for the first generation.
If you only want to keep a flock of pure breeds to breed each season for first generation olive eggers, then it doesn't matter much which breed the rooster is. Most breeders I've talked to say they get better olive results if the rooster is the dark layer, thus my rooster is a Barnevelder over Cream Legbar and Isbar/Marans F1 hens. Others were happy with a blue-gene rooster over dark layers.
But I also wanted a variety of shades and colors, so I know my Barney boy over white or light layers will produce cream and tan, which he does, as well as the greens and olives over the blue gene girls. That was one of my main reasons for keeping the dark layer vs. the blue layer rooster....my flexibility for color. With a blue gene boy, bred over any color layer, I will get shades of blue or green. No whites, tans, pinks or brown tints possible (if he is a 2 blue gene boy...or pure).
If you want to breed so that all your hens eventually lay blue or green, the work from the pure breed blue gene boy, your Ameraucana.
But, if you want to breed for longevity in olive for the line, using line breeding of daughters back to the father, it is better to keep the dark layer rooster (and his in tact brown wash genetics) to use repeatedly over the blue/olive generations. You keep the fresh dark wash genes passing over the pure breeds (F1 Olive) and then over the olive mixes (F2 Olive) to keep olive alive in the line rather than a diluting the brown wash each generation to where you get light green or even blue.
Generally, the boys are longer lived in fertility than the girls (who phase out by 2, or 3 years, where both quantity and egg shell quality can suffer)... A good rooster should last 5 years in fertility.
That's my thoughts. I've given more genetics below if you are interested as to why this works.
Good luck with your olive project
LofMc
Olive is created by a blue shell receiving brown wash. If there is no brown wash, the egg appears blue. If it is light brown wash, the egg appears light green. If it is a deeper brown wash (Marans, Welsummer, Barnevelder), then the egg appears olive.
Using a dark layer rooster....In your first generation Marans-Ameraucana, you will get light olive to medium olive eggs. Take those daughters and breed back to the Marans boy, you will get the opportunity for olive/dark olive about 50% of the time and brown/dark brown about 50% of the time
It really depends on the genetics of the rooster, and the receiving hen as well, how dark the shades go. With my Barnevelder boy, I find that the deeper brown passes about 50% of the time, so of my F2 Olive Eggers, I got 25% dark olive and 25% medium olive and about 25% medium brown (with pink overtones) and 25% darker brown...but not as dark as the dark Marans scale (I'm working with Barnevelder).
That means every time you breed back an olive daughter you have about 25% chance (depending on the rooster and hen) of increasing the olive depth.
If you switch the equation....Ameraucana rooster over Marans hens, your darkest brown will be the first generation for the brown genetics. I've heard that the hens don't pass the brown wash as well as the roosters, and I think I agree with that through my Barnevlder-Marans projects and some other breedings.
After that first generation of Ameraucana-Marans, you will be increasing the blue genes with each breed back until you get all offspring to 2 blue genes (I think by F3? or maybe F4) and decreasing the brown wash each generation.
1 blue gene layer generally lays a light blue egg. 2 blue gene layer lays a darker blue egg. Lightening wash will eventually get you to darker blue, ocean blue eggs.
You'd have to go back to the original Marans hens to refresh some brown wash to get to olive again.
My experiences...but I'm only about half way through my project...I've got some nice dark olive, some nice medium olive, but I've got to go back and renew my blue to ensure pure blue and a true green as I'm breeding for a full palette of color....got a nice Cream Legbar pullet in grow out for that.
