The scientist should expect that some bacterial will appear purple whereas other bacterial will appear red. The purple is a gram positive and the red is a gram negative. The difference is due to the differences in the nature of cell wall of two groups. In gram positive bacteria the cell wall is made up of thick layer of peptidoglycan that enclose the plasma membrane while in gram negative bacteria the peptidoglycan layer is thin and there is an outer membrane made up of lipopolysaccharides and lipoproteins that enclose the cell.
