4 colors just is not quite enough. And on many systems we have sprites to add that little bit of extra color needed to make everything stand out well enough to not be a problem. The Apple lacks sprites, but does have 6 colors to use instead.

2 colors is a special case, and so long as the pixels are roughly square and are of a decent size, 2 colors is also enough to do most anything minus color.

The second best thing about Apple 2 graphics is that it is artifact graphics! Normally, this kind of thing is not desirable. "Real" colors driven by some graphics chip offer a real color signal of some kind. And with that, offer more overall colors in more hues and often intensities. But, unless the video system is really fast, that color capability often comes with a price, namely pixels that are twice as wide as they are tall. The pixel art aspect ratio is a bit funky, and is often a poor match for many images.

IBM CGA, TANDY Color Computer 3 and some others do offer 320 pixel or greater 4 or more color displays. These individual pixels are nearly square.

The Apple, due to how artifact graphics tend to work, offers a 280 pixel color display that does allow a single pixel to be a color pixel. And it is a nearly square pixel! ( some TVs do mangle it all up into twice as wide as tall anyway)

In fact, it takes two adjacent pixels with the same value to get white or black; otherwise each pixel will be a color pixel.

This little detail is what makes Apple 2 graphics stand out, despite the machines age and very limited video system.

And the last thing about Apple graphics I really like is how using patterns in ways very similar to what one would do on a monochrome display yields a very plausible perception of more colors!

Really great pixel art is possible and we have seen a ton of it over the years.