Oh, OK, that's cool, hope it works, but I'm afraid it may not, because as the pigments are different, also the mechanisms to get them are, this means that having a breed which lays dark terracota eggs (high production of Protoporphyrin,
http://en.wikipedia.org/wiki/Protoporphyrin), crossed with one that produces green eggs (
http://en.wikipedia.org/wiki/Biliverdin) doesn't make the green pigment mechanism produce more pigment because they are from "different parts of the chicken body" so one would not affect the other, anyway I think you will get a green+brown mix color, since the chickens you will breed will produce both of the pigments.
Hope my bad English is readable and understandable enough for being understood (I'm from a country where we don't speak English, sorry).
But, anyway that's a very cool project that I would for sure try to! Good luck, then show us the results!