one of my hens has laid an egg with a lilac egg white

[Owllady]

do any of you know why?

They all seem really healthy, all laying each day etc. But i am a bit shocked by the lilac white and couldn't bring myself to eat it

it was lilac when I peeled it btw. I boiled some eggs yesterday and they were still in shells in the fridge, which i have just peeled top find a lilac one