While Googling around for indicator neons (rare in these days of LEDs), I found this at Jaycar:

"Would you believe it? After about 100 years of orangey-red neons we now can get blue and green ones! You'll buy one out of curiosity!
- Strike voltage: 82V
- Needs 270k resistor in series for 240V operation"

Cat #: SL2695 and SL2695

They've been around for a long time in Clipsal and HPM indicator mechanisms. Oddly, the Jaycar ones don't have the coloured phosphor on the inside of the globe which makes me wonder if they still contain neon gas or one of the other gases that create colours other than red, such as xenon or argon. I think all the noble gases can be used to create different colours.

I thought the Clipsal and HPM ones were done via coloured plastic lenses.

These Jaycar ones do appear to be based on gas.

The lenses are coloured though when they are swapped over to a mechanism that originally had a red, orange or yellow lens the colour rendition isn't good so they do use specially coloured globes for the cool colours. They charge accordingly too! You can also get mechanisms with clear lenses though these have the standard neon globe only, unfortunately.

I think the Jaycar site is correct - I am sufficiently curious to buy a few of these just for experimenting. My guess is that the 'neons' would chew less power than LEDs.

I have blue ones in a PSU / Reformer that I built in 2007. Blue is the "B" Voltage alive; Red mains alive; and orange B voltage fuse fail.

You can also have fun making a simple "Flash tester" (usually it wont flash with wax paper types) All you need is say 225VDC (like the Palec VCT) and some decent ohmage resistors, in neg & positive so there is not enough volts & current to kill, if you stuff up. You can pinch the volts from a radio.

As the cap charges there is a short "blink" and then the light extinguishes. DC should not pass through a cap. The intensity of the glow, is relative to the size of the leakage.

I would recommend IC clips & an MAS switch (Palec, does not have a switch. Neons also make Sawtooth wave, oscillators. DC can be pinched from a radio

Marc

Back in my early days of computer tech-ing we had purple neon-style indicators. We called them Thyratrons but I think that was wrong.
They are similar in size to the MTX90 neons. three legs and the purple glow was seen from the end of the tube.
We had them in their thousands in old paper tape and card punch equipment as indicators for the read and write bits in each byte.
The purple ones had a fairly short life, whereas the true neon indicators (orange - 2 pin) were much more reliable.

The list of colours can be seen here:

https://en.wikipedia.org/wiki/Gas-discharge_lamp.