`Cu_(2)S` is black and `Cu_(2)O` is red through `Cu^(+)` has no unpaired electrons and is colourless.

Explanation

Since `Cu^(+)` has `d^(10)` electronic configuration, d - d transition of the electrons is not possible and hence, `Cu^(+)` is colourless. The `S^(2-)` and `O^(2-)` ions present in `Cu_(2)S` and `Cu_(2)O` respectively can transfer their electrons momentarily to the metal ion (charge transfer). Hence, the compounds are coloured.