How do you tell the difference between black mold and mildew?

Color: Mildew is a filmy, whitish or light green residue that is forms of mold hyphae of various types of mold. Black mold, and I am referring to stachbotrys, is potentially toxic and is black or dark green in color. It grows in areas where there is standing water, often on horizontal surfaces, such as from leaking pipes. Mildew often collects on vertical surfaces in high humidity such as in bathrooms.