Complex sentence: The portrait is is composed in monchrome, muted colours, predominately blacks, greys and browns, excepting the white collar and sleeves, a patch of sharp red in the seat cushion, and reddish light falling on the leather of the chair.
Split into simpler sentences: The portrait is is composed in monchrome, muted colours, predominately blacks, greys and browns. The exceptions are the passages of his white collar and sleeves, a patch of sharp red in the seat cushion and the reddish light falling on the leather of the chair.