Preheat the oven to 350°F. Lightly grease two cookie sheets. Sift the flour, baking soda, and cocoa together. In a separate bowl, combine the oil, vinegar, food coloring, and vanilla.
Using an electric mixer, beat the sugar and eggs together until they turn pale and double in volume. Add the oil mixture and beat to combine. Add the flour mixture and buttermilk alternately in five small additions, starting and ending with the flour.
Drop the batter by teaspoons onto the baking sheets, allowing 1 inch between drops, as the cookies will spread. You’ll be making 48 cookies. Bake until the cookies are firm but not crisp, about 12 minutes. Transfer immediately to racks to cool.