Colour of smock chap uncovered (5)
I believe the answer is:
mocha
'colour' is the definition.
(mocha is a shade of brown)
I don't understand the rest of the clue.
(Other definitions for mocha that I've seen before include "Leather" , "Arabian coffee" , "Coffee flavour" , "Yemeni port; type of coffee bean" , "It may end up as grounds" .)