Certainly an uncommon piece, Roy.
I can’t recall seeing an opalescent sea green creamer before either, and I can’t currently find a pattern match in the Sowerby pattern books or my collection of reference photos.
The colour in the photo looks to be more ‘turquoise’ than green, but that may be because the opalescence seems much more pronounced than that usually seen in the Sowerby opalescent sea green pieces.
I presume that the creamer does not fluoresce strongly in UV light.
Fred