Widely used as a color-forming agent in thermal paper coatings, this compound reacts with developers like bisphenol A under heat to produce intense color changes, typically deep black or blue-black, essential for point-of-sale receipts, labels, and fax paper. Its leuco form remains colorless until activated by heat during printing, providing sharp image resolution and good stability. Also found in carbonless copy paper systems where it forms images upon mechanical pressure. Due to environmental and health concerns, especially regarding potential endocrine disruption, its use is being phased out in some regions in favor of safer alternatives.