You could very well be right - it's been a long time since I was commercially involved in TV repair and doing it all day every day. I'm pretty sure that they were argon filled, and I had this recollection of the discharge being white or blue/white, but the old memory is not what it was any more. Hell, I have trouble remembering what I had for breakfast these days - well, not quite, but you know what I mean !
Arfa