JTL i agree that it might be different for some Thunderbolt Display models. I'll have to look into that.
I play XBox One (original) on my LG Plasma - color depth doesn't seem to matter, and "regular" versus "PC" color gamut (the option on the XBox) changes the dither pattern on the TV but doesn't seem to do much else.
... actually now that I say that I've never really PLAYED with it set to "PC". I'll do that today at lunchtime and report back.