I don't find the chair itself, or the color of the wall, persuasive at all. Here is an interesting synopsis of the timestamped chronology of the killing that I found thought-provoking, though. I have not watched the tape all the way through and don't know whether it's completely accurate:
Check out the video timestamp timeline:
13:26 - Berg states his and his father's name. Seated in plastic patio chair in orange jumpsuit. Shot taken from a side angle.
2:18 - Seated in same chair, same jumpsuit, shot taken from the front. Berg identifies his family and where he lives.
2:40 - Berg is seated quietly on the floor in front of five masked men. All the men seem very well fed and the exposed skin rather pale for a bunch of islamic terrorists on the run. The middle guy appears to be reading from two pages of prepared text, although he is continually turning the pages over and over and over, his actions making it completely impossible for anyone to read anything from those papers. The video is too grainy to tell if the guy's mouth is moving.
2:44 - The shot angle has not changed - the middle guy is still 'reading' from his papers. Wild screaming starts on the soundtrack, but none of the masked men seem to notice it, and Berg is still sitting very quietly in front of them. He has not moved at all during these four minutes.
2:45 - the middle guy draws a knife from his jacket, pushes Berg over, and the camera suddenly zooms into such a tight closeup that the screen goes black. The timestamp abruptly changes here.
13:45 - the camera pulls back to reveal Berg utterly motionless, being manhandled by the attackers. An assailant with a black mask draws the knife across the throat, while an assailant with a white mask sits on the motionless body. The soundtrack has several people shouting "allahu akbar", but the opinion of native Iraqi speakers who have heard it is that the accents are NOT Iraqui, more likely arabic or arabic as second language.
13:46 - screaming escalates on the soundtrack yet the windpipe has quite clearly already been completely severed by the knife-weilding assailant with the Black Mask, the head being connected only by the spine. No screaming is physically possible at that point, yet it mysteriously continues, much the way it started. White Mask assailant still stitting on the motionless body, doing nothing.
13:47 - There is another in/out camera zoom and suddenly it is the White Mask assailant, not the Black Mask one, that steps away from the body, knife in hand, holding the head aloft. No blood anywhere. At this point, the timestamp and the camera angle abruptly change again.
2:41 - Berg's head held aloft by White Mask, different angle, no blood. Curious - what day is this? As previously noted, during the 2:40 through 2:44 period, Berg could be seen alive, seated quietly in front of his captors as they 'read' their statement.
13:48 - timestamp and shot abruptly change again. Now we get shot of head resting on top of the prone body, with a zoom on the body's severed neck. Everything is very clean, completely inconsistent with the forensic reality of decapitation.