Ya I am just unsure if the dark/light setting is really a proxy for colourspace. I get the feeling it is its own option that maybe uses video processing to get darker when "dark" is selected which results in an image which has crushed blacks and appears to be similar to what you would get if the wrong colourspace is selected on the HDMI range... (similar symptoms, but different vectors)
For me I have my cable box on 16-235, cause it will never output anything other than that.
I have my HTPC mostly left on 16-235 but toggle to 0-255 depending on what I am doing (when gaming for instance) - because of the way I have my HTPC configured in GPU/driver settings this toggling on the TV end delivers full colourspace when I need it, and leaves 16-235 unmolested if I am playing video content when I toggle back to 16-235 on the panny HDMI setting.
I then invoke "dark" mode only if I feel in the mood during a very bright day, where my image is already compromised and the dark setting seems to restore some of the black punch when viewing say, at 4pm with the sun streaming in...