I am having this issue as well with the drawings in Vault. When I initially check in the file, and Inventor creates the Visualization file (.dwf) during checkin, it looks like it should. But I then Update the .dwf by clicking the Update button in Vault, or by sending it to the job processor, it makes the shaded views a dark grey. I didnt have this issue with Inventor 2014.
I have contacted Autodesk about this issue months ago and they supposedly submitted it to the developers to look into. I am still waiting. I was initially told that nobody else is having this issue.
Also, a word of caution, I installed Update 1 for Autodesk Inventor Professional because I read that it had fixes for .dwf creation. This made things worse. After the update the .dwfs didn't show the models at all. I uninstalled the Update and I'm now back to the dark grey shading.
>>I was initially told that nobody else is having this issue.
Probrably not enough DWF users 🙂
The only reason that I wanted to use DWF format is because the Inventor Viewer is crap, i.e, it displays work features - not very professional looking when trying to market a product.