Thank you. I saw ortho, got boot. Broken fibula, cracked metetarcul and chipped ankle. You are right... See a doctor.
You will likely do more harm than good. If your foot is actually black then you must be seen today or risk amputation. Bruising is to be expected. A doctor will make sure the bones are properly aligned before/after casting. If they are not aligned correctly then they will not heal correctly. Sometimes a break will not show on initial xrays.