Aspergillus niger cultures have a dark brown to black surface due to the dark pigmentation of the conidia, but the reverse side is light-colored or white. Vesicles with two rows of phialides (biseriate) that cover the entire surface of the vesicle are seen microscopically. Phialides produce chains of rough, round dark conidia.
The top right image shows a contaminated culture plate with A. niger. The black colonies are A. niger. The bottom right image shows A. niger demonstrating conidial heads which are large, globose, and dark brown, and contain the fungal spores.
Images courtesy of the CDC