[2020] Why are my rocks black?

Do you have Painter/Repaint? Could be the mod is coloring them or bugging out and causing some random stuff. That's one reason I can think of that might do it.

We'll need a look at all your mods then. Otherwise we can be guessing for days. :P The easiest thing is for you to post your output log somewhere, so we can take a look. This guide explains where to find the log and recommends some places you can post it, since we can't attach files here on Steam.

https://steamcommunity.com/sharedfiles/filedetails/?id=463645931&searchtext=log

You should remove Fine Road Tool. Probably not related to the black rocks, but the original FRT is broken and conflicts with the newer Fine Road Tool 2, which you also have.

More Beautification is also at least partially broken. You should remove it as well.

These 3 I recommend unsubscribing whenever you aren't using them in the editor. They are really old and not working great, and they were never made for the game itself, just the editor.
- Building AI Changer
- Asset UI Category Changer
- Asset UI Priority Changer

I see a few local mods, which I assume are theme mixes for Theme Mixer 2. Try disabling these (or move them out of the local mods folder to test without them). They are:
- Central3
- Tukituki
- Wairona

Hmm, can you grab a screenshot of that? If you mean what I'm thinking of, that would be the LOD for the road showing when it shouldn't, which would be very strange. :S

Since things did change, it might be worth unsubscribing Theme Mixer 2 temporarily to see if that plays a role. I would unsubscribe and not just disable, as that's the only way to be sure the mod isn't doing something.

Oh, that was not what I expected at all, but that definitely looks all wrong. :S

What if you do a test on a new city? Does that also look weird or is it just this save?