It depends on the rooster that they are kept with.
I have first generation hatching eggs. The eggs come from a welsummer pullet covered by a blue egg gene blue wheaten easter egger rooster. So the pullets hatched will lay an olive egg.
Olive eggers can be accomplished in a few ways. You need a dark egg gene and a blue egg gene. The dark egg gene comes from either marans or welsummers and the blue egg gene comes from ameraucanas or easter eggers (if using easter eggers you need to know that they lay a blue or green egg) I do believe that there is another rare breed of chicken out there that lays a blue egg but I can't think of it right now.
ETA: Legbars and araucanas are the other two blue egg breeds I was thinking of.