After noting that Docile Hen/Handsome Dude three chicks looked a little red rather than rosy pink, I added greens, oatmeal and dry plain ABBA Green 92 to her choices.
This morning, when I checked their vents, this chick was clearly backed-up.Its vent was sealed with a thin coating which is almost invisible. I washed the vent with warm water and gently peeled the thin lacquer-like coating off and massaged the vent to make sure it was open.
After letting the chick walk in my palm, it relieved itself much to my relief too! Had that not worked, I would have hand fed it as once the chick is full, it naturally expels its wastes.