I saw this Taste the Rainbow Cupcake in a cupcake book that I have, it took me a few tries to get the bright colors but it was worth it. They make me smile.
1 box vanilla cake mix
1 can vanilla icing
Food coloring (I used red, blue, green, orange and yellow)
First things first; mix your batter as directed on the box. Then you need to divide your cake mix according to how many colors you are using. I used five colors, so it worked out to be a little less then a cup a color.
Once you have your batter in the separate bowls you can add your food coloring until you get your desired color.
Next you will add your batter to the cupcake liners, one at a time. What I do is add about 1.5 teaspoons of each color; it worked out to fill the liners half way. Once you have all the colors added you can place them in the oven to bake.
Once your cupcakes are cooled icing them with the vanilla icing.
McCormicks food coloring just doesn’t get the cupcakes bright enough. So I would recommend Wilton or a gel.
Also if using Wilton I would recommend buying no taste red.