As also mentioned in the article, the root problem is that for all the other pairs of colors defined by IBM the hue is the same and only the brightness varies, while for the pair yellow and brown both the hue and the brightness are different and many early implementers have failed to take this into account.
Brown is just dark orange, but what is interesting is that there exists no dark yellow, which is why IBM had decided to define the paired low intensity color for yellow as the more useful brown.
When the brightness of yellow is reduced without changing the hue, at some threshold the sensation of yellow disappears and the color is perceived as some kind of dark olive green. Changing continuously only the hue at low brightness passes continuously between a dark yellowish green and a greenish brown, without any intermediate color being perceived as yellow.
It seems that the sensation of yellow is produced by the approximate equality of the detected red and green components, but only when their intensity is high enough. This is similar to the sensation of white, which is quite distinct from the sensation of gray, even if these colors differ only in brightness.
Fun fact, human skin is orange - both dark and light. If you saturate the colors of photos of people of any race, everyone is orange. Some AI face detectors use this to help identify where people are in images.
Brown is just dark orange, but what is interesting is that there exists no dark yellow, which is why IBM had decided to define the paired low intensity color for yellow as the more useful brown.
When the brightness of yellow is reduced without changing the hue, at some threshold the sensation of yellow disappears and the color is perceived as some kind of dark olive green. Changing continuously only the hue at low brightness passes continuously between a dark yellowish green and a greenish brown, without any intermediate color being perceived as yellow.
It seems that the sensation of yellow is produced by the approximate equality of the detected red and green components, but only when their intensity is high enough. This is similar to the sensation of white, which is quite distinct from the sensation of gray, even if these colors differ only in brightness.