This is the second time that this happened. The first time I was actually messing with multiple things at once, all sorts of error messages etc. So I assumed it was something I did.
This time though it happened again with a clean code.
Saving and reloading fixed it 
So I have no save file to offer.
You found blüd island! Possibly something with your graphics card and the lighting? Still seems really odd.
You’ve entered Mustafar!
So far I only see this happening in the archipelago. So it is probably something I did.
Unfortunately at random.
Things that may be related:
The biome has an actual new block, sand. It is not just grass recolored. It has its own tags and drops, etc…
There is only 3 seasons instead of 4. And they are not spring…winter, not even in code.
This basically means that the terrain color map was invalid in some way. One case I could think of that might cause it is if the season palettes have different entries. E.g. if one season is missing a terrain color entry which another one has, if that season is first, it might cause the missing entry to be colored red.
They are all the same, copy and pastec. I’m yet to change the colors in different seasons. And when the terrain gets red, it is not just one tag, it is the whole terrain.
Another thing I saw is that the colors are using lower case hex digits, some are using upper case, and there is even one mixed like Ff. At least in old versions, landmarks were failing when using lower case, so I will also change it all to uppercase there too.
edit It failed again, even with all uppercase colors. I also noticed that it is not all plain red, the grass has a different shade, darker.
I guess because it is blending with the original colors? Maybe it is the season? Next time it happens I will skip time to see what happens in a season transition.
Another info about it. This landmark did not have the sand color (the same color as the terrain in the beachs) turn into red, although the rock colors did. This sand color is not listed in the landmark_blocks json, but the rock is also not listed… It is getting straight from the qb model.
Other landmarks in the map are red.
The only thing in the game that changes the terrain palette is the season renderer, so I would print out the palette being set in seasons_render_service.lua and see what it is when this issue starts occurring.
Hey @max99x I think I got this to 100% repro! (Unless the 10 times I tested was just a big coincidence ¬¬)
Starting the game (asc,archipelago,normal), and just skipping all screen does generate a map with correct colors.
Now if in the map screen I chose to reroll a random seed (clicked on the dice, then clicked again) it will be all red
I’m not sure what I should look for, so I just logged almost all lines I could in that file, this is a stonehearth.log from a normal map: stonehearth.log (49.1 KB)
And this one from a red map: stonehearth_red.log (50.0 KB)
Looking at those I did not see any difference, the colors seems fine.
We kept the hardcoded “spring” palette key as the default to support pre-season mods, but that caused this issue when there was no “spring” entry in the terrain palettes list. This should be fixed in the next release, and in the meantime you can fix it by using “spring” as the ID of one of your seasons.
