Why does mold/fungus come in such a variety of colors?

Here, a color guide to molds commonly found in the house:


If you see green mold, it could be just about any type of unwelcome fungus. There are more than a hundred thousand types of mold — and thousands of species of green mold. So what does the color green tell you? Not much.

Olive-green, brown, grey or black

These are common molds in the Cladosporium genus. Outdoors, they lurk on plant leaves. Indoors, they're often found on walls and insulation and can grow on damp carpet, too. They are linked to skin, eye and sinus infections. Very rarely, they can cause brain infections (fungal meningitis), according to the CDC.

Blue, green, or white

These molds, also common, belong to the Penicillium genus. You’re right if you think that a type of this mold was used to make penicillin many years ago. It’s usually found on food and walls.

Yellow, green or black

These may be Aspergillus molds. According to the CDC, people breathe in these molds every day, usually without getting sick. But those with existing lung problems or weakened immune systems may develop aspergillosis. This illness might entail coughing, wheezing and sinus inflammation.

Black or grey

These could be Alternaria, which is most common as an outdoor mold, growing around damp, dusty areas, soil and plants. But it has made its way indoors. In one study, Alternaria was found in more than 90 percent of house dust samples. Exposure to it may boost the risk of asthma.


The pink “mold” often seen in the bathroom in the form of a slimy, pinkish discoloration on sinks and tubs is actually bacteria, not mold. Specifically, it's Serratia marcescens. It thrives on soap and shampoo residues and is linked to urinary tract and respiratory infections. Don’t obsess about getting infected from pink bathroom slime, though. S. marcescens usually enters the urethra through catheters or the lungs through respirators, according to an article on the website of Scientific American magazine.


This mold, of the Stachbotrys genus, is the infamous “black mold” that some news reports have linked to severe health problems, including memory loss and lung bleeding. It's less common than the molds described above — and possibly less dangerous than news reports would have you believe. According to the CDC, Stachbotrys has not be proven to cause either memory loss or lung bleeding.

As to why they come in such a variety of colors, Scientists have come up with several different reasons why mold comes in such an array colors but can’t seem to nail down one over the other. There is a good chance a number of things are influencing the color of any give mold.

Colors of mold for example, vary regionally. The colors in the Pacific Northwest tend to be more green and blue whereas oranges appear more often in the Amazon.

Other studies indicate that the color of this particular fungi comes from its food source, genus, conditions under which it grows and it’s age.

While all of these things do contribute in some way, shape or form, mycologists (scientists who study mold) still haven’t been able to pinpoint one single reason why this mysterious fungi comes in all colors of the rainbow to this day!

/r/askscience Thread