Biological tissues are mostly colorless and lack contrast as shown in the unstained paraffin section on the upper slide. Stains provide contrast as well as differentiate among diverse tissue components and are often used in combination. The stained slide (below) displays how the tissue elements are revealed by the two stains, hematoxylin and eosin.
Hematoxylin staining >
Hematoxylin imparts a bluish color to the tissue elements.
Eosin staining >
Eosin imparts a pinkish-orange color to the tissue elements.
Image source >
Image modified from Abbasi, S., et al., Sci. Rep., 9:13392, 2019