To the OP: I would return it now if I could, you can always buy again once this problem gets fixed. Keep in mind how unresponsive Apple has been to their desktop customers this year. Who knows how long it will take before a fix is released. By then maybe you can pick up the machine as a refurb and save some bucks, or who knows maybe the 2013 Mini will be out by then with a discrete GPU option.
While this may be true, there are enough reports of white level clipping to indicate there *IS* an inherent flaw somewhere in the driver or HDMI compatability with certain devices and apprently it can't be corrected with the color calibration in OS X. Some who are reporting this issue are also indicating this was not a problem for those same HDMI display devices with previous Mini models they've owned, so clearly there *IS* something that needs addressed in the 2012 model.
I'm betting it's a driver issue as Intel GPU drivers have always had little issues here and there (the 23.976 issue comes to mind). I'm just not convinced that both Intel and Apple take the HTPC niche seriously enough to watch for these kinds of issues. If you're going to continue including an HDMI port on your machines, you better make sure they work properly!
The point is that clearly the QA process is slipping somewhere along the line, either at Intel or Apple.
I've heard enough to postpone replacing my MacBook HTPC with a 2012 Mini until this is resolved.
Shame on Apple for sticking their customers with Intel's immature GPU offerings by not giving us the option of a discrete GPU for the 2012 Mini.