In the original Teenage Mutant Ninja Turtles comic, all four turtles wore red masks.
Kevin Eastman and Peter Laird’s Mirage comic initially depicted Leonardo, Michelangelo, Donatello, and Raphael with the same red facial mask color. The turtles were distinguished by their names, personalities, weapons, and dialogue rather than by different mask colors.
The familiar color coding was introduced for the 1987 animated series and became one of the franchise’s most recognizable conventions. Leonardo received blue, Michelangelo orange, Donatello purple, and Raphael red. Those colors were then used extensively in toys, merchandise, later shows, and films.
Readers who know the franchise mainly through animation can therefore misremember the original comic’s design. The Mirage stories also used a darker black-and-white art style and generally had a more serious tone. Later comic continuities have sometimes adopted the television color scheme, but the first Mirage stories used red masks for every turtle.