I've seen them in translucent Red, Amber, Clear, Green, Yellow & now Blue.
Maybe it was another University/College Project!
Yup, add purple/plum colore too. I believe they were made By Petroleum Artifacts, OK.
They werent expensive at the time (125.00-200.00 in 90's?) I had one years ago in purple and sold it on ebay for 400.00. You just never know what someone will pay who doesnt know...I thought they were neat at one time too, now not so much.
Someone sell me an original Grey Crown.