In ZB 3.1, when I imported a texture it was applied to the tool.
Now in 3.5 it isn’t. No matter what texture I load, it isn’t displayed on my mesh. Why?
It is because you can now have different textures applied to individual subtools. Load your texture for your subtool via the Tool / Texture Map palette.
A good explaination here http://www.zbrushcentral.com/showthread.php?t=78501&highlight=beginner
Richard
Great! Thank you 
For changes introduced in ZBrush 3.5 see here:
http://www.pixologic.com/docs/index.php/What's_New_in_ZBrush_3.5