Eggs changed color?

So I have heard that there are only two colors of eggs: white and blue. Brown is a white egg with a brown pigment deposited on the journey down, and green a blue with brown pigment.

A couple of weeks ago a very weird thing happened. I have five girls who lay, one dark brown, one medium brown, two cream and one green. One day I got a medium brown, three white and a blue egg. No kidding.

All I can figure is that something in their diet or environment affected everyone's pigment depositing process - A couple days later everyone's eggs were back to normal.

Has this ever happened to anyone else?