How Much Does Color (Shade) of Brown Eggs Change?

I have a Red Cochin Bantam hen whose egg color ranges from medium to almost-dark brown. Today, I found a REALLY light brown (almost off-white) egg. I currently have 3 Silkie hens and 1 Wyandotte Bantam that are 17 weeks old. Is it possible that one of the newer hens laid this egg? Or can the color of a hen's egg really fluctuate that much?

I have seen my Cochin's eggs color change a little bit, but not THIS much. Now, I'm wondering if I should start doing the "butt check" on the new hens to see if it was one of them that laid the egg...