In salty water these cell walls absorb a green stain and turn green

This is the second of two microscopic images of potentially toxic cyanobacteria, Microcystis aeruginosa.  In both images, the cyanobacteria have been exposed to a green stain.
Image 2: Mycrocystis aeruginosa In water half as salty as seawater. The cell walls are breaking down and the stain has penetrated them, turning the colony green.