This is an adult male. Usually males are solid blue, but here in East Asia, the distinctive race M.s. philippensis has chestnut underparts. It is sometimes split under the name "Eastern Blue Rock-Thrush." However the two types intergrade and this individual shows more extensive blue underparts. 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).