Blue/green egg?!

[Sclark0012]

I have 16 hens, 1 laced Wyandotte, 1 barred rock, 7 RIR, 3 golden comets, 2 black australorps, 1 welsummer, and 1 ,what i believe is a black sex link, possibly mixed. Ive have never gotten a colored egg before, suddenly i found a blue/green egg! Is that normal?! Im super excited though!

 

[Sclark0012]

Pic for reference

 

[Sclark0012]

Possible BSL mix

 

[Tonyroo]

I've noticed if egg color was to develop it usually come from dark legged birds. So your guess is probably right.