In fresh water, these red cyanobacteria don't absorb a green stain
This is the first of two microscopic images of potentially toxic cyanobacteria, Microcystis aeruginosa. In both images, the cyanobacteria have been exposed to a green stain.
Image 1: Microcystis aeruginosa in freshwater. The green stain doesn’t enter the cells, which show up in red.