Marco, has created a free extension to help you see preview levels in Vegas Pro 12.
This allows you to enables Vegas Pro 12 to switch the internal video preview in between display modes, Either to at unaltered video signal or to a video signal with limited levels (“Studio RGB”). To do this it adds a “Sony FX Levels” as video output fx to the Vegas Pro project and changes or disables its presets, dependent on the selected preview option.
Thanks you to Marco…
Go to the web site here (free)