There are some that lay plum eggs. It's a colour that goes all the way through the shell, so there's currently some argument that the ones with that gene in the mix are likely to cross with another breed and provide either a dark reddish brown (crossed with brown) or a pinkish colour (crossed with white) or a lavender colour (crossed with blue). Apparently it's not a horribly common gene and often hides behind other, more dominant genes. I've not seen any proof of it; but, it's in some of the articles I've been reading about genes related to eggshell and bloom colouration.