Methylene blue isn't even used in Gram staining, so there's one counterexample for you.
Crystal violet, basic fuchsin, and safranin are all dyes which can be used in direct staining because they are cationic which means that they are positively charged. These dyes which are positively...
So that the cell can be seen, otherwise it would be very difficult to see the cells as they are somewhat transparent.
no