[Ron Ramirez]

As for the blue glow inside, if the blue appears to be just inside the glass, than the tube is probably OK. But if the glow is inside the tube elements and more purple than blue, then the tube is definitely bad.

Additionally: The bluish-pinkish-purple glow inside tube elements is caused by the tube becoming "gassy" (air has leaked inside, rendering the tube useless). A blue glow just inside the glass, not inside the tube elements, is not anything to worry about. This blue glow just inside the glass usually shows up only in audio output tubes.