Top two birds are of a fall or immature male showing pale tipped primary coverts and extensive pale mantle scaling. Females lack the blue color at all ages (bottom bird). Usually males are solid blue, but here in East Asia, the distinctive race M.s. philippensis has chestnut underparts. This race sometimes split as Eastern Blue Rock-Thrush. These birds inhabit remote cliffs and rocky slopes, but also urban areas and rocky shores. Formerly classified with the true thrushes, the rock-thrushes have been moved to the Muscicapidae (Old-world Flycatchers and Chats) family. Canon PowerShot SX60.
References:
Clement, P. & Hathway, R. (2000) Thrushes. Princeton Univ. Press, Princeton.
Collar, N. (2019). Blue Rock-thrush (Monticola solitarius). 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 https://www.hbw.com/node/58415 on 26 March 2019).