Yup. I want to have more exagerated heights in them. E.g., impassable can stick out more, difficult can just barely pass the tile boundaries, etc.
Going to be an iterative process here but already it's better. It's still a bit dark and muddy for my taste but I leave that up to others to decide for sure -- these worked well when recolored for the other two planet types.
EDIT:
Did a little touching up (adjusting contrast/brightness and increased the yellow components a bit) and it feels a lot better in-game now:
Still something a bit off, maybe I'm just not used to it yet.
It's still a vast improvement from the original tiles!
Also side note -- right-clicking on a tile will bring up the Tile Inspector -- it will tell you the terrain type, location, etc. This is on empty tiles, of course.