That's the problem; capturing this issue is next to impossible, as a screenshot won't do any good, and a camera won't do it justice. It needs to be seen in-person to really figure out what it looks like. The best I could do is come up with a simulated image with some work in Photoshop...
The issue WAS visible when using gaming on the Xbox 360, but I changed the "Color Space" setting to "Native" and the "Reference Level" setting to default, and it apparently took care of it, as I no longer see the issue there. The TV's color setting is also set to change depending on the displayed content, instead of "Native."
If I can't get a picture that shows it, perhaps I can explain it with one. Below is a screenshot of a metal grid in Just Cause 2. Aside from dark/shadowy scenes where the blotchy circles are visible over the entire screen in uniform rows and columns, grids like these are also where the problem is visible. Panning the camera up or down causes the stationary grid of blotches to become much more visible than if the image was stationary.
If it matters any, here's my current setup:
EVGA GTX 560Ti GPU -> Onkyo HT-S3500 HDMI Receiver -> Samsung PN51D550
I also connected the PC directly to the TV's HDMI port, and the issue is still there, so it can't be the receiver. Again, this issue is nonexistent when watching DirecTV or movies on my PC.
Is there anyone with a similar setup that would like to share their GPU and TV configuration settings?