regret I don't know m. I've had uranium green before, also a very nice blue grapefruit - neither of which were cased - I think my blue grapefruit is the only piece I still have.
It does appear though that this purple/amethyst can be cased.
Colour does appear to be variable - that large bowl shaped piece in the middle of Reynolds page 46 looks to be a lot darker than mine, or bats.
Perhaps certain shapes only were cased.