The article doesn’t say whether this appears to flicker on a CRT. Although pixel response time is quite good on a CRT TV, I remember it taking a while for the brightness of pixels to ramp down, which may dampen the flickering.
It flickers on a 50/60Hz CRT. As a kid, I toyed with "extra colors" quite a lot on C64, Atari, Color Computer 3.
There are three basic methods:
One is discussed here, cycle between two colors. Low contrast changes are best.
Artifact color is what the Apple 2 computers use, and that is basically using high resolution graphics to get colors when the small pixel size results in frequencies the NTSC color circuits see as color info.
The CoCo3 had a 640 pixel mode able to generate one byte per pixel, 256 color mode. A very nice find for a kid! The link is that graphics trick reproduced for others to see today.
This method is all about NTSC.
And the third way to get more color was all about PAL and I have PAL CRT displays now and should get PAL hardware to explore this method. Did not have access to anything PAL as a kid, sadly.
This method involved changing colors on alternating frames and vertical alignment of pixels. I could not find a reference image. This was probably not done much.
It's said later in the article that you'd need two colors with similar brightness to avoid perceivable flicker. CRTs did have some afterglow but it wasn't even for a full frame, let alone two.
