Yellow skin round eyes?

how long has she been like this (some chickens can have yellow skin).

I noticed it for the first time yesterday.  It is really quite a distinct change in her appearance, so think it's a recent development, or I would have noticed it sooner.

There is no difference in her behaviour that I can see.  Had a peep at her vent earlier, and it's nice pale pink, so she's not yellow all over.  Comb is still nice and red, legs are white. 
Its just a though someone has drawn yellow rings round her eyes, and touched in at the corner of her beak.  It's really strange.

She does get corn in the afternoon.  She's tucking into it right now.  But she's always had that since I've had her.  She's an ex batt I've had for just over 18 months.

If a chicken has jaundice, would all the skin be yellow?  Wondering if it's some sort of deficiency?  But the others are all OK, and nothing has changed in feed apart from they are getting a bit of poultry spice at the moment.