Hello,
The range of Dartington vases Volterra, Candy and Inkwell, were available in four colours, green, amber, smokey and jet.
The information is in "Dartington Glass, the First Twenty Yeras 1967 - 1987" (incorporating Wedgwood Crystal 1983 - 1987) by Stuart and Linda Smithson, published by them in 2007.
I met Linda yesterday and confirmed the black colour as being "Jet".
Nigel