Off colour in what way?? Off food / water? off her feet? Details might help!! Do you feed anything suspect (Raw potato, sprayed weeds)
We lost two of ours after very very short time 'off' we asked if the vet could autopsy but because they had to send it away, the courier had to be a pet cremation service and charged more than the post mortem! We decided we'd rather buy more hens with the money..
ps sorry for your losses, its always sad