The suggestion that you are some one else is the thing to strive for, not the concealment of who you really are.
Grim's skin had been sun-tanned in the Arab campaign under Lawrence against the Turks.

The Shereefian helmet is a compromise between the East and West, having a strip of cloth hanging down behind it as far as the shoulders and covering the ears on either side, to take the place of the Arab head-dress.
The khaki uniform had just enough of Oriental touch about it to distinguish it from that of a British officer.

No man inexperienced in disguise would dream of choosing it; for the simple reason that it would not seem to him disguise enough.

Yet Grim now looked so exactly like somebody else that it was hard to believe he was the same man who had been in the room ten minutes before.

His mimicry of the Syrian military walk--blended of pride and desire not to seem proud--was perfect.
"I'm now staff-captain Ali Mirza of Feisul's army," he announced.
"Ali Mirza a man notorious for his anti-British rancor, but supposed to be down here just now on a diplomatic mission.