A friend mailed me some Imperial Moth eggs last week, Eacles imperialis. They were quick to turn from a light green to transparent.
Within a few days of arriving they've started hatching. After a few quick nibbles they hold still a while, waiting for their spines to inflate (emerge?) and harden. These hard spikes will be their only protection early on.
I was also sent some Polyphemus Moth eggs so hopefully I'll be able to update on those too.