Why has my stainless steel cookware discolored?
Overheating or allowing cookware to boil dry can cause yellow, brown, dark purple, blue or rainbow tints on the stainless steel surface. Although harmless, these tints can spoil the appearance of the pan. To remove this discoloration, use a products like Barkeepers Friend® and a non abrasive cleaning pad. Wash with warm soapy water, rinse and dry. Discoloration is not covered under your product warranty. Please note that allowing a pan to boil dry can cause serious damage to your product and cooking surface, property damage and/or personal injury. Never leave a pan unattended and never allow a pan to boil dry.
To learn more about boil dry: Overheating vs. Boil Dry