So I turned the amp back on.
I really wish I knew how to take low light shots with a camera. This is the coolest thing I've seen since the first time I ever saw a tube light up. The blue is definitely on the inside of the glass itself, it's not coming from the filament or the plate. Now that I've looked more closely it actually swirls and snakes around on the glass a bit. It's also twice as bright as it was last time, the blue is almost as prominent as the filament glow with the lights in the room off.
They seem to sound normal. Cool stuff.