The Blackmagic Design driver is currently extremely limited with no option to select between YUV or RGB colorspaces.
You are stuck to their own "automatic" conversion" so if you plan on using a Plasma or LCD HDTV to monitor your work you are stuck with computer RGB range of 0-255.
For color I use a calibrated Pionneer Kuro 151 which offers me YUV 422, YUV 444, RGB 0-255 and RGB 16-235. I know it's not SDI and doesn't cost $45000 but it's very accurate and does a great job. Problem is that I can't use it properly with the Ultrastudio 3D.
We tested the box on current line of Panasonic and Sony HDTVs with the same result.
Now I have to get my Matrox mini out of the closet to work. This is very frustrating.
Regarding the gray that you were seeing at 16 with your display monitor, here is what we were advised.
Internally the color space is YUV, but it can translate the YUV to RGB. The translation can occur depending on the monitor. This would explain why you are seeing the grey at 16 and not white. Your monitor is receiving RGB at 0 to 255.
We inquired to see if there is a toggle or option to switch between YUV or RGB. Unfortunately, that is not an option that is currently available.
Hope that helps.
Blackmagic Design Inc. USA