The Schwaneberger Farben Fuhrer Colour Guide.

Notwithstanding the volumes of Colour debates here.
A fascinating journey into colour swatches from 1922.

Great to see the difference from Rose Carmine, to Carmine Rose, then Dark Carmine, and then having GERANIUM muscle its way in.

Vermilion (spelt incorrectly)

Madder Red, Bordeaux... lots of fascinating colour terms in this interesting monograph.

Note : MINIUM = ( Lead Tetroxide) "Red Lead"

Minium has been identified as one of the pigments at Angkor Wat in Cambodia.

Even in this example, try and separate 80 from 82...my eyes cannot.

Interesting. I never saw this one before. I see it on Amazon for $29 but none of the other usual sources.

I bought a copy of "Scott Specialized Color Guides for U.S. Stamps" to help with this. I used that book to calibrate my monitors and to ID the color codes with Photoshop. in doing so my scanner and microscope were both used so I can periodically validate their color reception. I can scan stamps and use Photoshop to ID the color. It's not an "exact science" as stamp condition will effect the color but it helps.

When my eyes are fresh, I do a pretty decent job but as time goes by I get worse. You would think it would be the other way around but as such I try to do this in short sessions.

I can see the difference between 80-82 just a slight shade off with 82 being deeper. Trying to do that with stamps isn't always as easy. Sometimes what works for very slight color differences is I lay a bunch of stamps on a black surface with good lighting via my Ott lamp and use the 10,000 yard stare not focusing on any particular item, using a wide field view if you will, like peripheral vision but not at the side. I can usually pick out the shades light to dark and rearrange them in order. Close my eyes for a couple seconds, then walk away for a few minutes, come back and do the same to check it.

Per my eye Dr., I've always had excellent color recognition and depth perception even with a slight nearsightedness. He used to tell me I should have been an engraver instead. I used to have very fine vision up close and could read the micro print in the loops on the side of the five dollar bill, but although my glasses prescription has not changed, time has caught up with me. I can't do the micro print anymore and it really pisses me off.

Yes, getting older is lots of fun.
Try swapping spectacles every time, monitor to catalogue.

Here are some blue hues, my eyes do not see #25 as Prussian Blue.

(121 Colours listed in this monograph)

Here is an interesting online color tool. It is an Convert HEX to RGB color convert but it also does a good job in illustrating the difference between hues (colors), shades, and tints.
https://colorswall.com/colors/tools/hex-to-rgb (edit, just noticed this site is having some issues today, link is fine, site is flakey today)

Try sliding the three (red, green, blue) controls on the left all the way to the left to set the the color to black (Hex #000000). Note that there is no such thing as shades of black, only tints of black (black with white added).
If you slide the red, green, blue controls all the way to the right to set the control to white (Hex #ffffff) you will see there is no such thing as tints of white, only shades of white (white with back added).

Consider color in terms of the visible light spectrum, note that there is no black or white color. For humans, color is strictly an expression of light. Stamps absorb/reflect specific wavelengths of visible light and this results in a stamp appearing a certain color to the human eye. This helps us understand the differences between a true color (or hue), a shade, and a tint. Shade is a color plus black, tint is a color plus white added.

It also helps us understand the total dependency of the ambient light source upon the stamp colors we perceive. Change the temperature of the ambient light source, and it changes the visible light spectrum we are seeing bounce off the stamp.

Don

Yes Don, getting "Bad Gateway"