pH is critical to determining the charge on both the dye and the tissue molecules. The overall colouration of the stained specimen is the result of the balance of the intensity of the hematoxylin and eosin.
Ionic bonding is the most important type of bonding that occurs in histology staining techniques. It involves electrostatic attraction between ions of opposite charge, one of which is fixed in the tissue, and the second of which is in the dye. Staining does not produce colour randomly; instead, the dyes exploit differences in the chemistry of the tissue and to various components.
In an H&E stain, you’ll usually see both eosinophilia and basophilia: the nuclei of cells are typically basophilic (blue), while eosinophilia is typical of cytoplasmic constituents (pink).