To reproduce:

1.Download and open attached project.
2.Open "VertexAlphaSceneLoader" Scene.
3.Go to Assets->AssetBundles/Simulation Mode and disable it.
4.Go to Assets->AssetBundles and enable Local AssetBundle Server.
5.Go to Edit->Project Settings-> Player and Enable "Optimize Mesh Data".
6.Go to Assets->AssetBundles and press Build AssetBundles.
7.Run the VertexAlphaSceneLoader scene and press load.
8.Press pause button to get better view of the loaded mesh.

Expected result: Optimize mesh data function strips vertex color from mesh correctly without generating visual artifacts.
Actual result: Optimize mesh data function strips vertex color from mesh incorrectly by generating visual artifacts.

Reproduced with : 5.6.0b10, 5.5.1p4, 5.4.4p3.

Notes: Could not reproduce on earlier versions because of compatibility issues. Not reproducible on PC because of how project is set up. Reproducible only on Mac machines. If Optimize Mesh data is disabled everything works as intended.