I've been playing some games through ScummVM, and there's a cool feature that lets you load the game using whichever graphics mode the software originally supported. It also lets you use shaders to simulate a CRT, because these bare pixels were never meant to be seen with human eyes. I thought it was fun to compare the art from the different versions.
The posted image is from the EGA version
Here is the CGA:
And Here is Hercules(Amber):
CGA was 4 colors out of 16 I believe, with the two default color sets like you say. But I only see 4 colors in the images, too. Maybe the white in the black green red yellow is actually yellow?