Types of the Afghan Army 1908
"When our war with Afghanistan commenced the Press burst out with a flood of anti-British articles with a Pan-Islamic flavour and on June 4th an Afghan envoy, General Mohammed Wali Khan, arrived with large staff and an escort of soldiers in scarlet tunics".F. Bailey in his book "The Mission in Tashkent" writes about the Afghan delegation in 1919.
Memoirs of the Soviet ambassador in Afghanistan. 1922:
"At the porch of the commandant's house there were eight horses in Kushka ... Next to it was a platoon of soldiers and two officers in a strange yellow uniform and round hats, they shone with large silver coats of arms: the dome of a mosque, two banners, sheaves of wheat and a Koran in the middle".N.A. Ravich. "The Youth of the Century"
And there is also a Soviet feature film about the Soviet mission in Kabul. There you can see the Afghan uniform, which, in my opinion, is depicted more or less correctly:
From 4:14 - a small scene of the battle of the Afghans against the British in 1919.
http://www.youtube.com/watch?v=5GXNh_Ixa08