IN A SMALL BOWL stir together flour, cocoa powder,and 1/4 tsp.salt;set aside.
IN medium mixing bowl ,beat the 1/4 cup softened butter with on medium to high for 30 seconds.
Gradually add sugar; beat on medium until combined.
BEAT on medium 2 minutes more, scraping side of bowl occasionally .
BEAT IN EGG,FOOD COLORING AND VANILLA.
ALTERNATELY ADD Flour mixture,and buttermilk, beating on low after each addition just until IN A SMALL bowl combined baking soda, and vinegar;stir into batter.