Does black-colored growth mean it is the especially dangerous kind of mold?

Color cannot identify the species or establish how dangerous a patch is. CDC/NIOSH advises addressing any indoor mold growth and the moisture that supports it, rather than prioritizing it by color. Ask for an assessment of the affected materials, extent and water source, not a diagnosis from a photograph. Do not dismiss a damp area because someone calls it mildew. If someone has symptoms or particular health concerns, a clinician should advise them about exposure and care.