I haven’t tried any version after the last stable alpha (so sorry if this has already been fixed) but in that one it was still hard to see details in terrain that was only lit by ambient light, so I’m going to resuggest my old solution to it.
If you’re worried that it will make the whole game darker then the effect can be made more discreet by moving the range of the ambient light closer to 1 (by for example changing 0.25 and 0.75 to 0.1 and 0.9, though I haven’t checked now if those are good values). Even a small change in shading on different sides helps.