The MELLS Journal
Black, white, green, yellow and pink mould: what the colours mean
The colour of mould does not tell you the species or how harmful it is; only laboratory sampling does. Colour does hint at where moisture sits and how long it has been there. Black and dark green growth marks surfaces that stay wet, white is often early growth or salt, and pink in a shower is bacteria, not mould.
By The MELLS technical team, Dubai. Updated 25 October 2026.
| Colour | Usually | Where it is found | What it points to |
|---|---|---|---|
| Black or dark green | Mould rooted in the surface | Silicone, grout, ceilings, walls behind furniture | A surface that stays wet for long periods |
| Grey or white film | Mildew, early growth | Window sills, shower curtains, painted walls | Condensation caught early |
| White and powdery | Mould on furniture, or salt on plaster | Wardrobe boards, leather, bare plaster | A closed humid room, or damp moving through a wall |
| Green or blue green | Fast growing mould | Walls, AC vents, stored boxes | Humid air more than a leak |
| Yellow | Mould on timber or fabric, or old staining | Wood, rattan, stored rugs, damp ceilings | Moisture held in the material |
| Pink or orange | A film of bacteria | Shower screens, floor grout, drains | Soap residue and standing water |
Does the colour of mould tell you how dangerous it is?
No. Many common moulds are black or dark green, and the same species can look different on different surfaces and at different ages. Only a laboratory can name what is growing, from a surface or air sample. The MELLS arranges sampling with an outside laboratory when a tenant, a landlord or a doctor needs that answer.
What the colour does tell you is useful all the same: where water sits, how long it has been there and what to check first. All visible mould is removed the same careful way, with containment, a HEPA vacuum and an antifungal wash. Anyone with breathing symptoms should speak to a doctor.
What does black mould mean?
Black or dark green growth means a surface has stayed wet for a long time. In Dubai homes it shows on bathroom silicone and grout, on ceilings above showers, and on external walls behind beds and wardrobes where the AC keeps the wall cold. Once it is rooted inside sealant or paint, cleaning only lightens it; the sealant has to be renewed and the wall primed and repainted after the cause is fixed.
What does white mould mean?
A flat grey or white film is usually mildew, mould at its earliest stage, which still wipes off. A soft white bloom on wardrobe boards, leather or timber in a closed room is mould on furniture. A gritty white crust on bare plaster is often efflorescence, salt carried out by damp, which dissolves in water. All three point to moisture.
What do green, yellow and pink growth mean?
- Green and blue green mould grows fast on dusty paint, AC vents and stored boxes, usually because the air is humid rather than because of a leak.
- Yellow growth appears on timber, rattan, stored rugs and ceilings that stayed damp after a leak. A yellow brown film near a window can also be old nicotine or pollen.
- Pink or orange slime in a shower is a film of bacteria living on soap residue. It is removed much like mould and comes back unless the screen and tiles dry between showers.
What should I do when I find mould?
- Do not dry brush it or sand it: that spreads spores through the room and into the AC.
- Switch off the AC in that room until it is dealt with.
- Look for the water: a leak, a blocked AC drain, a weak extract fan, or a wall kept cold behind furniture.
- For a small patch of mildew, wash with a detergent and dry the surface well.
- For anything larger, rooted in sealant or paint, or coming back, book an inspection.
Common questions
Is black mould the most dangerous kind?
Colour alone does not say. Many harmless and harmful moulds are black, and only laboratory sampling identifies the species. All visible mould should be removed carefully and its moisture source fixed.
Is pink mould in the shower really mould?
No. It is a film of bacteria that lives on soap residue and standing water. It is scrubbed off and disinfected, and it stays away only if the shower dries between uses.
Can I paint over mould?
No. The growth comes back through ordinary paint within weeks. The mould is removed, the moisture fixed and the surface dried before a stain blocking primer and anti mould paint go on.
Do you test which mould it is?
The MELLS arranges surface or air sampling with an outside laboratory on request and passes on the result as issued. Most homes do not need sampling to be treated properly.