selecting correct spiral balance

I am preparing to replace the spiral window balances for a window, but I can't determine the correct color to request. The existing balances are probably over 50 years old, and have an unfinished metal tip, instead of a colored tip. The window is a bathroom window, about 17" tall by 28" wide. There are 3 panes in each sash. Can you tell me which color tip to order? Thanks, Steve