What Color is Mold?

David J. Allen

I spent the better part of 2 ½ years learning about mold and indoor air quality because my child's life depended on it. Now I help others avoid ever having to experience the same thing. The mold industry suffers from conflicting opinions and I do my best to distill loads of data into something practical and useful. I love hearing from and helping readers. • "A house desecrated by mildew, mold, or fungus would be a defiled place to live in, so drastic measures had to be taken." — Leviticus 14:45

While black mold is the type of mold that people are most familiar with, the invasive fungus can actually grow in a variety of different colors.

In fact, most mold colonies that you’ll come across will contain several of them.

Oftentimes, a group of mold spores may even start its growth as one color, then transition to an entirely different color as it develops. In total, there are dozens of distinct colors of mold, many with their own preferred environment, region, and habitat.

“There are thousands of species of mold and they can be any color.”

American Industrial Hygiene Association, March 2013 Position Statement (Rev. 03.18)

Here, we’ll examine some of the most common mold colors, looking at when and where they’re most likely to appear and what you should know about them.

Why does mold come in different colors?

Scientists have managed to identify a few theories on why mold can appear in so many different colors. One popular belief is that mold spores take on colors based on their main sources of nutrients in the area.

It has also been proven that factors like humidity level and amount of light exposure can play roles in which shade a mold colony assumes.

These ideas are backed up by the fact that certain colors of mold tend to primarily show up in specific settings and parts of the world.

There may be other factors as well. Some fungal biologists theorize that mold may also change its color as a defense mechanism.

For example, studies show that darker-colored mold is better protected against extreme temperatures and ultraviolet light than light-colored mold is. In truth, scientists are regularly learning new things about mold growth, and there are still many uncertainties surrounding the fungus.

Black mold

“Black mold” typically refers to Stachybotrys chartarum, a highly toxic mold that has made its appearance in many media outlets. Black mold has been the villain in many a mold horror story.

Stachybotrys chartarum, or black mold, is considered the most dangerous of the commonly found species of mold. and it can appear in houses, apartments and offices..

It, like some other molds, produces mycotoxins routinely. If black mold is molested or interfered with, it may, in defense, increase its production and output of mycotoxins.

Black mold is usually identified by its slimy, wet spread of dark green-to-dark-black goo.

Since it is impossible to determine whether a mold is indeed Stachybotrys chartarum without the use of a microscope, you are likely far better off simply assuming that if it looks like black mold (Stachybotrys chartarum), it is black mold.

Deal with it with extreme caution. If you are unsure of how to properly and safely remove it, consult a professional.

Black mold is most often seen during construction and remodeling, or when appliances are changed out in a kitchen, bathroom, laundry facility, etc. At any point when the sub-flooring of a room is exposed, or the backsides of wood cabinets are made visible, black mold may be found.

It does however appear in other areas—including inside of a bathroom vanity with a dripping sink—and merely needs excessive moisture over a prolonged period of time in order to grow.

Black mold loves dark, damp, and humidity. It can appear on the wallpaper, walls, or the flooring or subflooring of your bathroom, laundry room, or any other part of your home that has remained excessively damp for prolonged periods of time.

The common mold type is known for its rapid growth and resilience to harsh and changing conditions, and it typically takes quite a bit of effort and persistence to remove it completely once it’s taken a foothold.

Blue mold

Unlike other types of mold, blue mold actually has somewhat of a positive connotation, solely for the fact that it’s used to create the invaluable antibiotic penicillin. However, that doesn’t mean that it’s any safer or healthier to be exposed to than other colors of mold.

Despite blue mold’s value to society, breathing in its spores can still result in allergic reactions, lung inflammation, and sinus infections.

Blue mold is most commonly found growing on food, but it may also appear on any wallpaper, carpeting, or insulation that has been exposed to water. Usually, blue mold will have a powdery appearance, and in some cases, its hue will start to transition toward black or green if it continues to be exposed to moisture. 

Brown mold

Brown mold is typically used as a catch-all term for several different species of mold, all of which are known to commonly show up on wood surfaces. You may find the fuzzy dark fungus growing on plywood, on your deck, or around your home’s foundation.

At times, it has also been known to flourish on damp windowsills or between the tiles in bathrooms.

“Visible mold growth on surfaces can appear slimy, sooty, velvety or fuzzy and can be a variety of colors including blue, green, gray, brown, white or black.”

New York State Toxic Mold Task Force Report, Dec. 2010

Most of the time, brown mold will be more dangerous to wooden structures than it will be to your health. However, it does release spores, which can result in sneezing, coughing, and other allergic symptoms when inhaled. Brown mold is also notable for its powerful and distinctly musty odor, making it easier to notice and locate in many instances.

Gray mold

While gray mold isn’t one that you’re likely to find inside your house, you very well may encounter it in your garden. Gray mold can affect virtually any plant species, and its growth usually begins as one or more small white or gray spots.

Over time, the fungus will spread to cover the entire surfaces of the leaves or flowers, sometimes changing color and eventually causing the plant to wilt. Gray mold also regularly appears on fruit, and if you’ve ever let a batch of strawberries sit for too long, you can attest to that fact. 

In most cases, gray mold is only harmful to plants, but it has been known to occasionally affect people. Typically, this comes in the form of an allergic reaction known as “winegrower’s lung,” due to the mold’s tendency to develop on wine grape plants.

If you find gray mold in your garden, the best thing you can do is remove any infected flowers, leaves, and stems. To prevent it from showing up in the first place, though, one effective strategy is to space out your plants. That way, they’ll have plenty of room to dry out after a rainstorm or watering.

Other colors of mold

Black, blue, brown, and gray are some of the most common mold colors, but they’re far from the only ones in existence. You may also come across green mold, orange mold, pink mold, or purple mold, and that still doesn’t cover every type.

One thing that almost all of these colors of mold have in common is their love of moisture; that, and the fact that if they’re left alone, they’ll spread.

So, if you want to keep these funguses out of your home, keep a close watch on any dirty, humid, or dank areas. And, if you do come across a developing mold colony, be sure to take action quickly. Whether you choose to remove it yourself or hire professionals, what’s important is that you don’t put it off.