High voltage CT ( blue/red ) does go to ground.
the confusion is with the heater winding. both the 5V (yellow) and 6V (green) are CT. We do not need to use this but it can be done. the idea is with most rectifers the whole heater winding is at your high voltage. we need to tap off it to the rest of the power supply this can be done at one end or the middle (CT)

For our supply, just use the end and tape off the CT.

for example for a 5AR4, 5U4, 5R4, 5V3, 5V4, OR 5Y3 The heater in this case the 2 yellow go to pin 2 and 8 the high voltage (Blue 340VAC I think) go to pins 4 and 6 the high voltage CT ( blue/red ) to ground ( cap Neg) and we tap pin 8 for our high voltage to the choke we use pin 8 rather than 2 because if the above rectifers have a seprate cathode it is internaly connected to pin 8...John