An wild insight appeared. Whenever I do terrain tiles I kind of run off doing wild structural variations. However, somehow a tiled look with a few well made blocks always looks better. Maybe the eye likes structure.
So, this time I started doing the usual varied rocky hill thing. No matter what colors I dressed it up in, it just looked out of place. Mario needs structure, blockyness, a rigidity. But I didn't want to use the same tile for entire mountains.
So, I thought, what if I keep the structure of the original block design, but treat it as if it was a mass produced thing which has gotten exposed to wear and tear?
To do this effectively, I needed one more color so I could go a little quiet where I needed to. I nearly went for a dark to, but it killed the simple graphical feel. I hope that the yellow-orange which I added don't.
Anyways, I started playing up and down detail strength, pushing in and out chunks.
I think it works. The horizontal highlight on the top gets more emphasis, and the grit 'underground' won't distract as much or flicker/distract when scrolling horizontally.

The bushes look mighty simple now though. Maybe I should toss in that dark green Helm(?) suggested. But I don't want to slip down a slope and add aliasing or elaborate softening shadows to stuff.
Thinking of punching my yellow-orange up a bit in brightness (or brown down?).