Operating system: Windows-10-10.0.20201-SP0 64 Bits
Graphics card: Radeon RX Vega ATI Technologies Inc. 4.5.14736 Core Profile Context 20.8.2 27.20.2001.16003
Broken: version: 2.91.0 Alpha, branch: master, commit date: 2020-08-25 19:28, hash: rB396d39c6b904
Worked: (newest version of Blender that worked as expected)
Short description of error
When undoing a simple brush stroke in sculpt mode, the mesh colors some random faces in red. if you switch to another workspace and then go back, the color will be gone.
Exact steps for others to reproduce the error
Open Foot.blend, draw brushstroke, and undo. The red color should now be visible.