I've only been raising chickens for about a year and a half, but my hens have started to run away more and more frequently. I have two Easter Eggers, two Rhode Island reds, and two Plymouth Rock hens. They are free range, and have always stayed close to their coop. Their coop is regularly...
Araucaunas and Americanas and are breeds with black variety feathers that can lay blue-green eggs, among other colors including brown, yellow, white, and pink. If your hens have any Araucanan or Americanan genetics, that would be a fair explanation as to why the eggs might be that color.