Wikipedia has dark grey text on a white background for the primary text. Headers are in actual black. I found another 6 shades of gray that are all used in multiple places on the site.
I found 5 shades of the primary color blue.
A good color palette uses many colors but feels like few. Wikipedia is doing a great job of this.
The article actually kind of addressed this with the shades, and I think that's what a lot of non-designers miss; having several shades of the same color adds a lot of variety without looking cluttered ("feels like few" as you said).
But I don't understand the point of the shades, then. Why not go for the real thing? Why not use the exact same color, and it will not only "feel like few"? What's the actual advantage of using different shades (besides making the work of the web designer seem more difficult).
It lets you display more granular information. You can have light blue buttons with dark blue text, as well as solid blue buttons, to convey "primary" and "secondary" CTAs for instance.
You could try to display the same amount of info in less color, or even black and white (maybe outlined buttons, bold/regular fonts in the text), but color variation looks "good" to the majority of eyeballs.
I found 5 shades of the primary color blue.
A good color palette uses many colors but feels like few. Wikipedia is doing a great job of this.