Acid And Basic Dyes
Acidic dyes are anionic which means are negatively charged and thus react with positively charged and repulsed by negatively charged materials.
They are called as negative stain and are attached to the background and stains it and cells are colorless.
Basic dyes are cationic which means are positively charged. Therefore, it reacts with negatively charged materials.
They are used in positive staining and are used to color the cells against background. Positive staining dyes are absorbed by the cells and thus gives color to cells against the background.