Thanks for your replies... As an update, the hen who had been showing a pale comb for the last few weeks now is exhibiting a nice bright and rosy one. I have no way of knowing for sure, but I'm thinking that is was her who had this 'lash', and that she should be ok now. Hope I'm right.
This afternoon I was cleaning out the poop from the droppings board and I found this (egg shown for size comparison):
It resembles a date, but is much harder. While I was pretty certain it was not a date (I don't know how one would have ended up in the coop), I cut it open to be sure...