Joy;
I agree with Trish. Been thinking about it and it's one of two things albeit I am not an expert... I have read about this in the past but for the life of me I can not pin point where. The experience appears to be purely environmental rather than biological, and a harmless thing, just rather unattractive.
If memory serves me correctly, there is a thing about certain breeds, possibly, when they start to get their seasonal laying habits back in gear after the winter slow down, sometimes the eggs will be discolored. (which is biological) And, of course inks or dyes could cause this effect as well.
As long as the girls are eating and staying busy and pooping normally, they should be fine, it will pass the more frequently they lay. I remember someone commenting about the off colored yolks and eating them as well with no ill affects. Don't know if I'd be that daring but???
Is it one particular breed or various ones? How is there shell color coming out? My birds lay dark shelled eggs when they first start laying again. I've been told that the longer a hen holds in her egg, the darker the shell will get on a non-brown egg layer.