I don't think rejuvenating the tube will help. It looks like the blue gun is stuck on (I think just blue, although maybe green as well). That could be a H-K short in the tube, or it could be a problem on the chassis, usually the drive transistor on the neckboard.
The easiest thing to do is to pull the drive transistor off the neckboard and see if it's still stuck on, or if you lose blue. If it's still stuck on, you've got a short in the tube, if it goes away, you've got a chassis problem, likely that drive transistor. You can also check the resistance from the H to Blue K on the tube... it should be open (or high resistance, check H to Red K to get a baseline value).
If it's low resistance, a rejuvenator won't fix the short, but what you can do is create an isolation transformer for the heater by cutting the traces to the heater pins, then take a wire, wrap it around the ferrite flyback core 2.5 times (I think), then solder each end to the heater pins. This creates a transformer to make ~6.3V AC for the heater voltage, but it's AC coupled, so it doesn't affect the picture. The way it's originally connected, it's DC coupled, causing the gun to be grounded (full on).
Oh, and if the tube is shorted, you should test the transistor as well, since a lot of times the shorted tube seems to take out the transistor.
DogP