Versions 5.6 and earlier:
During Edit Mode, the mesh turns whitish. However, upon validating the modification, the mesh returns to its intended original color.
Version 5.7:
The mesh turns whitish, but when the modification is validated, the whitish vertex colors are permanently saved to the mesh. This can only be reverted by using Edit → Undo (specifically for the bone manipulation). Simply entering “Bone Manipulation” mode without making any changes triggers this bug.
It appears that a simple visualization mode is becoming embedded/baked into the mesh vertex colors.
Current Workaround:
The only solution I have found is to perform all bone manipulations in version 5.6 and then export the file to version 5.7.