how to Change color for back faces or flipped normals

```
hi every thing works fine but i was trying to identify backfaces
i have to review several .obj models
if i turn of mesh.isDoubleSided = false
i can not see the model properly is it possible to change the color of back
faces so that we can identify them easily

```

Original issue reported on code.google.com by `simha....@gmail.com` on 22 Feb 2015 at 4:55

Start by locating the renderer's handling of mesh.isDoubleSided and the OBJ face data, then inspect how back faces are classified. Done means back faces can be assigned a distinct color while the models remain visible for review.

Written by the indexing model from the issue text.