This is because there are a ton of different versions out there with different colors. And the reference to "classic" is actually a more recent specific release with that name, not the original oldskool version.
In this case the correct answer should have been that there is no definitive correlation between the colors and the categories, because it depends on the specific release. The wiki stating the colors with that much confidence is simply wrong, it may be there is a edition with those colors, but other editions use other colors.