Toenails can take on various colours. The black colouring of a toenail is often the result of some sort of trauma. The blackened appearance is actually the accumulation of dried blood under the nail itself. Sometimes, a black nail will completely detach from the toe and fall off. Not to worry, a new one will grow back in time. In rare cases, a black or brownish colour of the nail may be caused by melanoma. If this is the case, the earlier treatment is begun the more promising the results. All black toenails should be evaluated by a podiatrist as soon as they are noticed. Better safe than sorry.