Do you mean why their originating Quechua lay colored eggs? I mean, I know they lay them because of their descent of the birds we got from South America, but beyond that, not entirely sure. Perhaps it was a certain strain of junglefowl, a sport, or something else crossed into the junglefowl that caused it. . .
All I know is, much of the diet of the original blue and green egg layers in Chile aided in their colored eggs. Often it was the copper in their diet.
Yes, today. I learned it while going through the Araucana thread - A lot of mention of the natural food sources like Quinoa are rumored to aid the blue egg color because of their copper content. Some even say Sweet Potatoes do the same. After bringing it up a couple times on BYC, people began to confirm it.
I've yet to try it myself, as whenever I have Quinoa around, my Araucanas aren't laying. . . But this summer I'll be growing some, and taking photos to have some visual evidence and data in seeing if it actually works, and how much.
I plan to have Quinoa in their daily feed starting this fall, so regardless if it truly does enhance the blue color or not, they're gonna eat it.