I have one Ameraucana hen who lays a light blue egg. She rarely lays now that she is approaching 9 years old, but when she did, late in the cycle, the egg would fade to what appeared at first glance to be white. So, same color just lighter in the cycle. Same with all other hens, generally. And...
No, they don't change egg color. What they start laying is what they will always lay, though it may fade in color as the laying cycle progresses prior to the molt. Your Easter Egger (or Ameraucana, if it is one) is the one who laid the egg-the others can't lay blue or green eggs.