Answer:
The color of the hens egg shell is not determined by the feed. The breed of the chicken is the determining factor of the egg shell color she will lay.
You can influence the color of the yolk inside the egg somewhat by a diet high in beta carotene.
Araucana chickens produce the blue egg because they extrude a bile high up in the oviduct as the shell is forming. Other breeds like Rhode Island Red hen eggs have the color introduced to a white shell further down in the oviduct. A fresh brown egg can have the brown color removed with some light scrubbing soon after laying, you cannot scrub off the blue of an Araucana egg as it goes all the way through to the inside of the shell. Look at the inside of any brown egg...It is white. If you look at the inside of a blue/green egg, it is the same inside as outside.