Do not diagnose mold by color alone
Dark staining can have several causes, and different molds can appear in a range of colors. If species identification is necessary for a project, that belongs in the assessment/testing side of the process rather than a visual guess.
When to call
Call when dark mold-like growth is widespread, keeps returning, follows water damage, appears on porous building materials, or may extend into concealed spaces.
Related next steps
Understand assessment vs. remediation · Possible hidden mold · Mold removal in Round Rock