So you are saying that the plates should not be the same color as the filaments?
I guess not. I never messed with sweep tubes until I repaired an amp for a guy. I had someone test the tubes for me and my cave man method was good enough to spot the duds.
That amp had several meltdowns before I overhauled it. The owner said it the transformer would grunt and it looked like daylight coming out of the side. He had one of those good aluminum foil fuses in it.