In Photoview, changing transparent amount is straight forward. What is the equivalent in Vis? I see IOR and trans color as called out in this link, but I am not seeing just an opacity type slider:
Bunkspeed Pro Suite 2012 Review - Desktop Engineering
1. does it exist?
2. enhancement request, possibly?
Just a guess but it is possible that varying transparency may be something only available in the Pro version, not the standard version included at no charge.