Dark green to black patches, slimy or fuzzy, spreading in irregular blotches rather than a uniform stain. In Calgary homes it turns up where moisture lingers: basement wall corners and carpet edges, bathroom ceilings, window sills fed by winter condensation, attics with poor ventilation, and behind drywall wherever an old leak was never fully dried.
Two cautions. Dirt, soot, and a dozen other mold species look nearly identical, so eyes alone cannot confirm what you have. And the worst growth is usually the growth you cannot see, inside wall cavities and under flooring from a past water event. If you found a patch, or you smell mustiness but cannot find the source, get it looked at properly before disturbing it. Nonstop Restoration inspects for free across Calgary, Airdrie, Chestermere, Strathmore, Okotoks, and Canmore, using moisture meters and thermal imaging instead of tearing your walls open.