‘Sad colours’ were well understood and well used back in the C17th. They were actually rather beautiful nuanced tones of a range of shades; to quieten them down and settle them into interiors created with polished materials and dyed fabrics. It was a sophisticated response to decorating hierarchy and as such is as useful today – but could we call this subtle grey green Sad Stone?  Of course not these days, so we have called it Gladstone!