Thanks for the great info, Thornygardener! I'd love to see some pictures of your blue fish - I can't imagine mine getting that large - the heron unfortunately usually takes them before they reach even 10 inches.
I was also thinking that I haven't heard of a blue goldfish, but wanted to hear from those more experienced than I. It doesn't have any netting, and I'm not sure it has a zipper down the back. If it does, it's not very pronounced. I am going to have to take a good look once I can focus more clearly this morning. It's still new to the pond and a bit skitterish, and swims away very quickly before I can get a close look or picture.
The shape of the head definitely resembles pictures I've googled of the shusui. Which is different - more sloped - than my other koi.