Mold and mildew are fungus that need moisture and a food source to grow and spread. Mildew is mold that prefers fabrics and textiles while other molds prefer to feed on paper or wood. Mold and mildew grow on linoleum with constant water exposure, such as from a sweating toilet tank.
Mold comes several different colors. The black mildew on the toilet is commonly a harmless fungus that is attracted to the water there. The purple mold staining the floor may well be the very same mold, although possibly a different species. In addition to black and purple, mold may be green, orange, yellow, gray or pink.
Before you can see the mold growing in your bathroom, you can generally smell it. It has a musty odor that persists through cleaning. Any areas of the room where water stands can be a potential breeding ground, and the damp musty smell often associated with not only bathrooms, but kitchens and basements as well, is a strong indicator of mold. Mold also reacts to UV light, showing up blue under a black light.
Mold can be cleaned away using a cleaner with enzymes that actually eat the mold and mildew. These are sold commercially as fungicides. For new mold that has not yet penetrated into the porous surfaces of flooring, baseboards or drywall, wipe away using bleach or ammonia. Keeping the area as dry as possible can help with its resurgence, such as using the fan while running the bath or shower and periodically drying areas that tend to get wet. Using a dehumidifier in your home to lower relative humidity is also very helpful in eliminating mold.
While you may assume that all black mold and mildew encountered in the home is "the" toxic black mold, this is not the case. Any mold can be harmful to your health, but toxic black mold, or Stachybotrys, is actually greenish in color. It prefers cellulose materials as its substrate, such as drywall. Laboratory testing is necessary to determine if your black mildew is toxic. Any mold may cause allergic symptoms if there is enough of it present in the home, and all mold should be eliminated when found.