What does the purple "X" mean when clearing terrain?

[josh.minkler]

I noticed when you select some terrain for clearing, the "X" above the tile is red if that tile can't be reached, yellow if it can be reached, and green if it's currently being worked on. I selected some tile for clearing, and the "X" is purple now for some reason. What does the purple "X" mean?

[Rayvolution]

It's actually black, but with transparency it may be coming off purple on your screen depending on what tile it's over. :)

But it means the tile was recently under threat, and nobody will work on it until they feel it's safe again. It should transition back to red or yellow shortly. The duration depending on how much it was under threat.

If this happened inside your village, it could have just been a trashy slime or something that spawned. Outside, it's usually monsters who got too close overnight.