RGB LEDs for power indicators (again)

Originally, I had been planning to provide a "standby" switch, i.e., a switch on the high-voltage DC power, separate from the heater power (for the tubes).  There would have been separate LEDs for "power" and "HV", and at one point I thought it would be clever to have the two LEDs be colours within an RGB LED.  However, how to power the LEDs was an issue, since 5v DC power is only available when the preamp is on...

In any case, the Internet talked me out of standby switches; instead, there will just be a "mute" switch.  So it was back to one plain power LED for each of preamp and power amp, presumably red.  I planned to power these LEDs from the heater power lines: which are not referenced to ground except through the "hum bal" pots.  So, the LEDs would be fed from primitive DC power supplies (diode, capacitor) running across the two heater lines.

But especially considering my use of tube rectifiers, it's nice to have a light that comes on when the HV is active, after the warmup period.  And if that is the blue, and heater power is the red, within an RGB LED, then the colour will start out red, then shift to purple as the amp warms up.  At power off, the blue will stay lit and gradually fade as the HV discharges.  This is a lot of good information (wouldn't have to be RGB of course, that part is just a cute gimmick; could just be separate LEDs).  But to use RGB LEDs, everything must be ground-referenced (common cathode assumed).  So the circuit from the heaters becomes two diodes, one from each heater line, to a capacitor which goes to ground; the red LED resistor feeds from the junction of diodes and cap.  The red LED brightness will vary as the hum bal is adjusted.