The classic red velvet cupcake contains just a hint of unsweetened cocoa powder, as well as buttermilk, white vinegar and vanilla extract. Once you have those in the batter, the cupcakes can be tinted any color – including the classic red, which is where the cupcakes get their name. However, you can also combine blue and violet gel food coloring to get these unabashedly patriotic blue velvet cupcakes. Once they have been coated in white vanilla buttercream frosting and some colorful sprinkles, they are ready to be enjoyed!
Source Traceys Cullinary Adventures