It would look great in black!

Gray (from the stone) would be another good option.

I hope you are painting the shelves, columns AND the mantel. I chose dark because I think it will help the TV to blend in and not stand out.

I agree w @2014Diane. You want the TV to recede, not be emphasized, so dark is the way to go. Try Kendall Charcoal or Wrought Iron by Benjamin Moore. One other thought - in addition to color, the other challenge you seem to have is that the styles of the elements of this unit seem very different (the stone, the columns, and the mantle) all appear to have very different style elements from each other. If so, paint will help them recede but will not fully solve it. If it's in the budget and you can come up with a design you like, could you design a false front to put over much of it, and then mount the TV over it all? I recently did something similar to hide and awkward corner fireplace (see photos of the before and then construction

Sorry Yolanda - I hadn't finished comment above and accidentally submitted and now it won't let me edit. Anyway the false front thing: mine isn't done yet (sorry for the construction mess - major remodel underway) but here's some photos to give you a sense of what I'm talking about. The box you see above the not-yet-installed mantle is where the TV will go. First photo is how it used to look. Second is with built-ins removed and new false front installed over it all.