System Information
Operating system: Darwin-19.2.0-x86_64-i386-64bit 64 Bits
Graphics card: Intel Iris OpenGL Engine Intel Inc. 4.1 INTEL-14.3.9

Blender Version
Broken: version: 2.83 (sub 9), branch: master, commit date: 2020-03-14 18:05, hash: rBa210b8297f5a
Worked: 2.81

Short description of error
The vertex paint opacity slider under the viewport overlays menu doesn't do anything since 2.82. It used to show the exact vertex colors without any shading overlaid on top.

Exact steps for others to reproduce the error
Switch to Vertex Paint mode on the default cube, paint on one of the corners, then try and adjust the vertex paint overlay slider in the viewport overlays dropdown.