That looks like it should work just fine. You can also paint your back board to more fit in with the wall decor if you like. Probably not so much an issue being hid behind the big TV SET all of the time.
On mine I was not able to find any thing to mount my back board to studs anywhere so I used the MOLLY BOLTS in the four corners of the back board that spreads out behind the thin walls... This was for my 26-inch TV in my fifth wheel...
I leave my large HDTV mounted all the time during the cold winter months. I just make sure the room has warmed up to normal temperatures for a short time before turning on the big TV screen. No problems so far doing this but we don't have extreme temperatures here where we live in Northern Neck Virginia.
Your install Looking good... Thats a big TV set haha...
Roy Ken