This is a female. Males are similar but show a maroon shoulder patch. Usually confined to the Himalayas this species exhibits altitudinal migration moving to lower elevations in winter. Often listed under the name "Himalayan Parakeet" it has recently been documented in China. This species was formerly considered to be a race of the similar Gray-headed (Finch's) Parakeet (P. finschii) of SE Asia. Rothschild’s Parakeet (Psittacula intermedia) formerly considered a race of Slaty-headed is now considered to be a Plum-headed Parakeet hybrid. Canon PowerShot SX50 HS.
References:
Collar, N. (2016). Slaty-headed Parakeet (Psittacula himalayana). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from http://www.hbw.com/node/54567 on 16 September 2016).
Rasmussen, P.C. & Anderton, J.C. (2012) Birds of South Asia. The Ripley Guide. Vols. 1 and 2. Second Edition. Smithsonian Institution. Michigan State University & Lynx Edicions, Washington. D.C., Michigan & Barcelona.
Rasmussen, P.C. & Collar, N.J. (1999) On the hybrid status of Rothschild’s Parakeet Psittacula intermedia (Aves, Psittacidae). Bull. Nat. Hist. Mus. London Zool. Ser. 65(1): 31–50.