I'm sensing jest here, but for those not in the know, the rover makes these patches with its Rock Abrasion Tool:

https://www.youtube.com/watch?v=INlSAGD01q8

The purpose of the abrasion is to grind awway the outer rind of material on the surface of the rock. We do that because that outer "skin" has been eroded by sand, wind and even moisture for up to billions of years. Geologists would like to see the fresh, untouched interior of the rock, so Percy abrades the outer few millimetres. In the case of this abrasion, we got a truly glorious result in doing so.

I need to write up a FAQ for the whole process and science of abrasions that this rover makes, but I'm a little delayed right now by all the amazing stuff this mission keeps throwing at us...