Ink N Drink Marker Marker with color changing ink for coffee and tea cups to indicate when a drink is cooling. 5 brand new markers per order Ink N Drink marker writes dark blue but changes to bright green when a drink hotter than 150F enters. As drink cools, ink slowly fades to blue to indicate drink is cooling. When completely blue, drink is at 150F which is deemed a safe-for-the-tongue temperature. Coffee and Tea are brewed at 190F or greater. Works best when written on paper cups. Effect varies for porcelain. Made in the USA. Color Changing Marker | Promo video: http://youtu.be/qWORQbA8l-w