Cold foiling is a cheaper finish than hot foiling. It's not as bright and shiny as a hot foil (which can look a bit over the top if there's too much of it IMO).
Ask your print supplier for some cold foil swatch sheets. These are a great help because you get a pretty big difference between end product and the CMYK that you print over the foil. Eg 0,15,70,0, which is quite orange when printed alone, gives a nice yellow gold effect when printed over a cold foil.