In the late 80's, I had an interesting incident with an Atari ST that I've never really understood.
I was using some graphics software that I recall was very similar to the way Microsoft's Paint still works. It may have been "Degas". It was still relatively unusual to have a colour monitor at that point, but I had one - Philips I believe. It connected via the Atari standard monitor connector.
I created my own colour using an RGB value - bright lime green. Approximately equivalent to 128, 255, 0.
After some time of painting with various colours, my eyes started to tire and I turned down the brightness on the monitor. The lime green colour seemed to brighten! I turned down the brightness some more - the green got brighter!
Eventually, the brightness of the monitor was virtually black. What I realised was that the green was remaining the same and ignoring the overall brightness setting of the monitor. This gave the impression that the colour was in some way brighter than the monitor was able to produce. It was quite disconcerting at the time.
It seems that in some way, is was directly controlling the RGB values of the guns, bypassing the electronics of the monitor. How was that possible?
EDIT: I feel that my description isn't really putting across the experience, so I have mocked-up some equivalent screen-shots as if it happened on Paint.
Here I am, painting with my new Lime Green colour:
I turn down the Brightness:
Experiment with turning to the lowest possible brightness:
In the 2nd and 3rd images, I have replicated the effect by just redrawing the green shapes in the original colour, after having dimmed the image across the board. It is a remarkably good representation of the effect that I saw.