When a corruption damages a dirt stair (the one that the Bricktrons make when they are digging a quarry) it will turn a bright purple.
I saw the same thing happen to a tree stump today:
Just to confirm I've also seen this happen a lot when tree stumps take damage from explosive barrels - I've had entire hilltops covered with pink tree stumps.
Hey guys, just wanted to let you know we're aware of this issue. The reason is actually kind of funny; if there are stumps or other "non buildable" things in a repair task and a Bricktron destroys it, the repair tasks tries to create a blueprint that doesn't exist to re-build it. Happens to tree stumps, quarry stairs, etc.