Preheat oven to 350 degrees F.(175 degrees C) and grease pan.
In medium bowl, combine melted butter with sugar and mix well. Add vanilla, cocoa powder, salt, food coloring, and vinegar in that order, mixing between additions.
Whisk in the eggs one at a time, mixing well between each. Fold in the flour.
Bake for 30 minutes in preheated oven and cool completely before cutting into squares.