The blue/green eggs seem to follow their own rules. I read that the color can be enhanced by carotenoids (yellow and green veggies), but you really need to look at the inside of the shell to see if it's a brown coating that might be changing the outside color, or if it's the base shell color that's different. My EE lays a green egg that has no brown coating. That's the color of her shell all the way through. She laid one yesterday that was so pale, it was almost white and the NewHamp laid one without the usual bloom that makes her very round eggs look pinkish. Guess my girls are still a bit messed up. Hope that Denagard works! --When I get it.
I have heard that the Marans eggs will get darker, especially for new layers. People talk about them 'kicking into gear' color-wise.
In the movies, strange things are always hidden in the basement.... monsters, aliens, bodies... Never heard of chickens in the basement!