Kastrup / Kastrup-Holmegaard only made uncased Gulvases in dark green, dark (Bristol) blue and amber, between 1962 and (as far as I can tell) approx. 1967/68.
As far as I've ascertained all Gulvases produced in smokey grey, clear, and light blue were made in the UK, apparently under license from Holmegaard - but I've no evidence to back this up or indicate which company that may have been. Of course, there were also factories in Italy knocking out copies at the same time.
My own personal stance is that until someone can turn up some evidence of the licensing of the Gulvase to anyone else, examples not in the three original colours would be safest viewed as copies.
As a sidenote, cased ones were produced in yellow (both with white interior and yellow interior), white, blue, red-orange, red, light-to-mid green, and very rarely the dark green used for the uncased examples. Anything not in these colours is certainly Italian.... as are some in these colours. It's a bit of a minefield! :lol: