Repro steps:
1) Open my attached project
2) Load the scene (and turn off 2D view if it's enabled)
3) Notice the plane turns red and soon returns to white color
4) If you didn't notice focus the view and plane and double-click the scene file to reload it
5) Play the scene - notice the mesh stays red

Workaround:
In the script VertexColorInstance copy-paste Start() with all the lines in it and rename to Update()