To Suggest Depth
This quilt design looks three dimensional.
The Block is two shades of green and two shades of brown. The dark green and the dark brown are seen as shadows. If something is casting a shadow, you brain tells you it must be three dimensional.
This time the contrast between the colors has been reduced and you no longer see shadows. The design looks flat.
You may think this is a repeat of the first quilt. But it's not.
If you check the shadows in the first quilt, you will notice that they fall in every direction - left, right, up and down. in this quilt the shadows are all to the right and down.So this quilt is more realistic in its use of shadows.
However, the lesson is it doesn't really matter. Your brain sees three dimension either way.