They're also transparent, the image uses stained samples. An aside about staining, the dyes created for the textiles industry during the industrial revolution

They're also transparent, the image uses stained samples. An aside about staining, the dyes created for the textiles industry during the industrial revolution had the neat side effect of advancing biology greatly. As each dye binds to different things in a cell it allows scientists to glimpse the inner workings of the cell.