I have read that tigers will use spicebush, Christie, so it could indeed be a tiger egg.
In my experience the eggs are pure green, so green they blend in with the leaf they're on, but I also know that the color of butterfly eggs varies from one individual to the other. Giant swallowtail eggs can range from greenish yellow to orange, and pipevine swallowtail eggs come in various shades of red.
Here's a picture of a tiger egg -
{{gwi:463258}}
Sherry

My prickly ash isn't far away. Hope it wasn't a Giant Swallowtail that missed. It's still an egg this morning. I think it's probably a tiger. If I can't tell what it is when it hatches, I will post a photo.

Update - It wasn't a swallowtail at all, but some kind of hornworm. It's very light green with a dark tail.
It's crawling around a lot. I'm not sure it's happy in the container with the spicebush leaves. I put some tomato leaves in there to see what it would do.

I've tried raising TSTs on spicebush, both on the plant and in containers. The cats eat it for a few days but always end up dying. I recommend avoiding using spicebush for TSTs unless you have extra eggs for experimentation.

I've never found a tiger on spicebush,but recently found two fifth instar cats on cucumber tree (Magnolia acuminata?) This was a first for me and I'm wondering how frequently they use this as a hostplant?