Did monochrome CRTs used in terminals have a reddish hue when they were displaying white color?

I am trying to replicate the colors that old monocrome CRTs displayed in a modern UI and Web pages.

Good luck. Each type had its own phosphor mixture, each with distincts different main emission line and often secondary as well. In addition those lines could be widened by using secondary materials.

The colors I use are white rgb(220,217,217) and rgb(0,0,0) trying to replicate black & white terminal output of a crt. The text is rgb(220,217,217) upon a rgb(0,0,0) background.

This may already start by black not really being black back then - real black is hard to create, even today. Just think of all the effort done with OLED to get a nice black background.

As you can see white has a slight redish hue upon white color makes more eye pleasing and easier to read the text.

Wiki has a nice table of some common phosphor materials, providing their main emission lines in terms of wavelength. By taking a look at the page about Spectral Colours it shouldn't be hard to turn whatever wavelength you intend to use into a colour (hint, peek into source to get RGB).

For example a 12" amber screen in my office uses a P3 type with a main emission at 602 nm. According to the table 600 nm is #FE5D00 or (254, 93, 0).

Except, when using that colour, it seems way more orange than the real thing. This is due secondary effects and dimming by the glass itself, but also the fact that RGB is only a weak approximation of perceived colour (out eyes are neither structured that simple nor evenly. So with modern hardware (255, 191, 0) may approximate way better.

But are these colors up to the ones that Old Monochrome Crts displayed, especially the ones used upon serial terminals?

Well, they may.

I tried to use pure white (rgb(0,0,0)) but they were pain to look upon, thus I hyad to compromise.

Sure, white is today, as with black, way cleaner - plus the fact that modern screens are usually way brighter than old monochrome CRT. Modern screens are not only colour, but also optimised for modern multi colour details using many different level.

Trying to technically recreate some generic B&W CRT doesn't make much sense - especially if it's intended to work in a modern environment (aka window).

Bottom line: Find a colour combination that looks good to you and use it.

Emulating CRT colour is a difficult subject. Sure, you could simply decide some RGB color for your definition of white and decide another color for black.

If you had asked about emulating IBM 5151 monochrome monitor that uses a green P39 phosphor, it emits light at wavelengths that add up to a color you cannot express as a standard RGB value, because standard RGB uses BT.709 colourspace and P39 colour is outside the gamut of possible BT.709 colours, so you would need to find a closest possible colour you can express in RGB.

That said, since you want to emulate a white phosphor, white and different tones of white are obviously reproducible using standard RGB values.

If the exact phosphor you want to emulate is not known, then we could assume a white P4 phosphor. It's very near the white point of daylight, so it appears a bit cold white or bluish white.

But there are two or three different formulations for phosphors called P4, as compatible options without cadmium. They should be quite close to the original.

To further complicate things, the P4 phosphor is not a single compound that emits white light, but it's actually a mixture of two compounds, one that emits bluish light and one that emits yellowish light, and when added together in suitable ratio, the resulting mix is white light.

As someone already mentioned, different compounds may decay differently after excitation. It might appear as cold/bluish white, but if bluish emission decays faster than yellowish emission, the color will shift from cold white to warm white while it fades.

Also different compounds wear and age differently, it may well be that the terminals you used were cold white when new, but warm white when used if bluish compound wears out faster than yellowish.

You also make a good point on the brightness setting. It could be that depending on the brightness setting of the original monitor, the bluish and yellowish compounds may not have balanced output, it could be that at high brightness the output is more cool blue white and at low brightness the output is more warm yellowish white.

So if you want to emulate a CRT, there are many deep rabbit holes you may get into, and emulate flying electron beams, their magnetic deflection, focused beam size, and how it excites phosphors of different kinds and what light the phosphor mixture outputs at diferent excitation levels and how the outpuy decays, and in the end, what will be the resulting color and brightness in RGB you can express.

So, it is possible the monitors you are talking about did have a warm white or reddish output when you saw them. Pick a suitable color temperature and convert it to RGB; modern monitors using BT.709 primaries should have neutral white defined at D65 white point, or 6500K, so higher colour temperatures will appear bluish and lower color temperatures will appear yellowish or reddish.

The classic P4 "white" phosphor is bluish, but there are many standard formulations with different colors, including different shades of white. And, of course, the CRT manufacturer was free to use a non-standard formulation. So, the answer is no, not generally, but there may have been particular terminals with reddish displays.

The "original" black-and-white TVs and the first (monochrome) CRTs were a very dark gray-green background (about #28 47 1F) with phosphor that glowed very light blue (#DC FA FF).

Green phosphor was found to be a little better for terminals; IBM used it by default for so long that the color is often associated with mainframes.

Amber phosphor succeeded green because of the annoying magenta afterimage from spending too much time in a "green screen".

The next color advance was "paper white" -- essentially, blue-white phosphors that were filtered. These turned out to be annoyingly dim.

Full-color RGB CRTs had their own problem: addressable RGB phosphor dots had to be behind a mask to preserve color integrity (beyond the scope of this answer), and the individual color dots on CRTs were too large to comfortably view up close.