One of my favourite people and teachers in Montreal, Margaret de Linden said to gather up scraps of white thread, roll them into a ball, moisten it well with saliva, rub the blood specks with it and later with a sponge moistened with water go lightly over it. A friend, also a nurse in the same class said to her it was terribly unsanitary, but who cares, it sure works well!! I now use underneath hand finger protectors, little ovals of tough sandpaper backed with sticky stuff to keep them in place on fingers so need to use this interesting technique less but it works with all colours of fabric when you need it.