What is a red eye coffee Starbucks?

Red eye coffee is an old term used to describe tea with a shot of espresso, or put another way, it's coffee with the addition of espresso. A red eye is slightly less potent than a black eye but both are stronger drinks made by mixing caffeine shots (espresso) with either black or Americano style coffee. A black eye is made exclusively from Espresso Shots while the red eye only adds strength to regular brewed cafetiere drip coffees. The still-brewed coffee should be about the same color as the Espresso Shot which makes up 30% of its volume.