Performance drop when changing vertex colors

I am making a game with procedurally generated levels and geometry (long trails from some game objects).
Unfortunately, Unity works in a wrong way with modification of mesh attributes (position, colors, etc).

Another posts about the same problem:
http://forum.unity3d.com/threads/11...loss-in-Mesh.CreateVBO-for-dynamic-meshes-IOS
http://forum.unity3d.com/threads/111870-Procedural-mesh-update-slow-on-iphone-4

I'm creating a regular grid mesh (440 verts and 798 tris) that is something like a half-pipe with regular grid. I want to colorize a subset of vertices dynamically.

Here some stats from my iPhone 4. Rendering a mesh takes 0.5 ms, but when changing vertex colors each frame (for each vertex) i get 9ms. Using double buffering from posts above improves it to 6ms.
Using colors32 instead of colors not making any difference.

Actually, when I modify any attributes on mesh - vertices, normals, tangents, colors, I get spikes and renderer utilization about 6-9ms.

Maybe it is possible to achieve the same effect using vertex shaders?

 

Setting vertex colors is relatively slow because Unity has to convert the Color array into something usable. Fortunately Unity 4 has Mesh.colors32, so you can use a Color32 array instead.

--Eric

 

I get same slowdown even when not touching the colors array. I also tried storing colors in tangents.
When I comment just one line in my update:

Code (csharp):

1. mesh.vertices = localVertices;

the mesh render takes 0.5ms. Just assigning new values (but with the same tris count and layout) to any of mesh arrays cause huge performance drop. That's strange...