Shamas or Magpie-robins Copsychus spp.

Indian Robin The Indian Robin, Copsychus fulicatus, is a shama or magpie-robin native to the Indian subcontinent but has several subspecies over its range. Males are black with a white shoulder patch (not always visible) and red belly and undertail. The tail is usually held upwards to show the red, unlike that of the Pied Bush Chat with its white undertail. Females are brown. Shown is the nominal subspecies from southern India.
Oriental Magoie-robin The Oriental Magpie-robin, Copsychus saularis, native to the Indian subcontinent and part of Southeast Asia, also can be distinguished from the Pied Bush Chat by often holding its much longer tail upright (but not in the above image). It also has a white shoulder patch and white belly, rump and undertail. Males are darker than females, which can be quite pale in some subspecies.
The two lovely photos above, taken in India, are with thanks to Dr Harsha Vardhan Reddy.