Rings the things that matter so you can tell them from the scenery: every rock you can mine or bump into (and their like on every planet: ruins, stromatolites, icebergs, chimneys), enemy worms and nests (shown above trees) and your own land mines. Items lying on the ground show as dots on the map and minimap. Decorative rocks are left alone. Only the sprites change, so it costs nothing while you play. Colours and on / off per kind in the startup settings.
Providing the player with new tools or adjusting the game interface, without fundamentally changing gameplay.