I don't get very many opportunities to inspect the eggs since they almost always have the fuzzy butt of a parent parked on top of them. But this morning both parents were out of the nest so I took a look. I was expecting to see five eggs, but instead I saw this:

It was quite a surprise, since I wasn't expecting the eggs to start hatching until approximately Tuesday. The incubation period is 16-18 days but it usually takes about three weeks for the eggs to start hatching because the parents don't start sitting on the eggs right away. It's only been 17 days since the first egg was laid, so they must have started sitting immediately this time.
If I've figured out the parents' genetics correctly, this chick is either a normal grey male or a cinnamon female. I think it's probably the male since the eyes look so dark, but I'm not sure that I can accurately identify a newborn cinnamon.