Hello,
Powell, Richardson, Webb and Stuart (and possibly Walsh Walsh and Webb Corbett) all used versions of dark green. This small bowl/vase is not Sea Green, but rather a dark green. Compare known Sea-Green by Whitefriars/Powell with this and you instantly see the difference.
I believe you will find a similar, wrythen, example by Thomas Webb within an article written by Lesley Jackson in the Glass Association Journal No5, 1997, where she uses a copy of an advert from The Pottery Gazette as an illustration.
Cheers, Nigel