4-Ethoxychrysoidine Hydrochloride is primarily used as a biological stain in microscopy to enhance the visibility of cellular structures. It is particularly effective in differentiating tissues and cells under a microscope, aiding in detailed histological studies. It also functions as an acid-base indicator with a pH transition interval of 3.5 (red) to 5.5 (yellow). Additionally, it is applied in the textile industry as a dye for fabrics, providing vibrant orange-red hues that are durable to washing and light. Its staining properties are utilized in research laboratories for various analytical techniques to identify and study specific biological components.