Offhand; muted grey/light brown for the building, white and perhaps red/blue for the robes (create a focal point, and symbolise the intensity of arguement in otherwise quiet and neutral surroundings); you could also add a bright-spot at the top of the window(I presume it's the window?) to try and emphasise the general unimportance of such arguements (pettiness, right?) in the face of the issues of the 'real' world. Or you go to a more dark/surrealistic route and depict it as a petty arguement as the world outside is literally falling apart; although I suspect this wouldn't be as well suited given the general feel of the picture so far and in particular the angle.
Really good conveyance of emotion/body language on the characters, BTW; might want to redden up the cheeks etc and add to that.