Blue Gas in Tubes - Why? Is it Bad?

Well, since tubes are supposed to be a vacuum, why should you want any extra gas? If it were desireable, everyone would do it, not just a few rare cases.

If you go to the KR Enterprise site they will tell you this is bad and will give you the reasons (I don't recall). This is the only source where I have ever heard that this is negative but as they make tubes perhaps they have a point????

I use an ARC VT-100 with an LS-9 (ss) preamp. My tubes glow orange. I tried a Morrison ELAD (ss) preamp which made the tubes glow bright blue -I disconnedted it immediately.
I don't know if my tubes "had gas" but I wasn't taking any chances...

It is not a concern. If anything, it indicates a tube that has less gas in it. The elements may glow orange, but the blue is more of a fluorescent glow in the whole tube in the dark. See audioasylum--the tube guys there know this is true.

Try reviewing some of the guitar forums such as PRS forum and Fender discussion page, and Les Paul forum. There is a lot of info on tubes and your question. I have always had a blue glow in my power tubes Fender and Marshalls when they are biased properly. You can get some Bias Probes on ebay fairly inexpensively. Invest in them and you may see some improvement in the peroformance of your equipment. I am in the chicago area and what some of the shops want for biasing your tube amp is ridiculous. Not uncommom to pay $75.00+ in this market. You can buy a bias probe or equivalent for less. Most of the tube amp musicians/techs would love to respond to your questions, at least on the typical guitar amp power tubes. Go for it!