[bedifferent]

What does this mean? She is a starlight hen, quite dark feathers. I have noticed recently that she has a slightly purple comb developing. She is eating and laying. Any idea if anything might be wrong???

[Aunt Sally]

If her comb is slightly purple it means she is not getting enough oxygen into her blood.

Does her breathing sound a bit laboured or rattly?

There are quite a few conditions which cause lung problems most of which require antibiotics so keep a good eye on her to see if the blueness goes ortherwise, vets I'm afraid !

[Bodger]

We have had some very cold nights and it could be a touch of frost bite. This happens quite a lot, especially with birds that have large combs. Leghorns can be a veritable nightmare.
It could be circulatory problem of course but I wouldn't worry about it, mainly because there is little or nothing you can do about it if it is.