How lucky to have EEs in your life! My little Elfi is my best hen friend, she's so clever and lively. She lays a blue green egg, very pastel, but sometimes favors a lighter shade and sometimes darker and maybe speckled a bit. When I've tried to read up on this, it seems like all eggs start out white, and gather pigment in the oviduct; if it moves through very quickly, the pigment may not stick, so if she is laying at an above average rate, she may have eggs moving through so quickly they aren't picking up much color. Elfi has darker eggs when laying less frequently, paler when laying often. I notice this with my Maran as well; when I'm getting a lot from her, I'll get lighter eggs. If she's giving an egg every other day, they're much darker and speckled. Keep in mind I've learned all of this from the internet, so it could be way off, but it seems like a reasonable explanation. Fresh eggs daily has a great post on egg color, and is a great blog to follow.