Here are photos of three different eggs, brown, blue and a greener one.  The greener one is greener because brown was added to the shell later.
All three eggs unbroken:
The inside and outside of the brown.  Notice the lack of color on the inner shell which indicates brown laid on after formation.
This is the greener egg, notice color is bluer on the inside.  
This is the blue egg, the color is more intense on the inside because the "bloom" has lightened the outside of the shell.
This simple test of cracking shells indicates that blue eggs start out blue, no color is added later.  If the bird in question truely did have some sort of change egg color, the egg would be green as brown would have been laid on after blue.
Also I do not think that this would be a case of the bird being a "chimera" as chickens only have one working oviduct.
I truely believe this is a case of "operator error".  Perhaps the other easter egger this person owns lays the blue egg.  And, all chickens stand to lay their eggs, they can't get them out otherwise.