Color tinting for mesh markers

Fix bug where marker message color was overriding material color.
Allow color tinting for texture mapped material and non-texture mapped.

Shows color tinting for textured mesh and untextured for (0,0,0,0), (1,0,0,0.5) and (0,0,1,0.5) marker colors:
![screenshot from 2014-04-28 19 30 26](https://cloud.githubusercontent.com/assets/652867/2824245/c86619f8-cf2d-11e3-843d-7abbdb550c9b.png)