I was inspired by seen Rainbow Cupcakes in many blogs & websites & thought of trying them. However I used only two colours & selected colours as Red & Green. Red & Green perfectly match with this Christmas season.
Here is my recipe.
Ingredients(12 nos)
100 g Butter in room temperature
100g sugar
100g flour sieved
2 eggs in room temperature
1 tsp Baking powder
½ tsp vanilla essence
Red & Green food colouring
Method
Preheat oven for 350F.Line the baking pan with cupcake liners.
In a bowl combine flour & baking powder, keep aside.
Beat butter & sugar together in low speed for 2 minutes. Then gradually add eggs for this mixture and mix in high speed for about 2 minutes until the batter become smooth.
Then add vanilla essence,
Also gradually add flour while beating.
Once it becomes a smooth batter, divide to two portions. Add few drops of Red coloring & make one portion in red colour. Do the same with other portion & make it green. (If you use more colours, divide the mix accordingly & mix with colours.)
First fill the ½ of cupcake liners with Green coloured batter.
After that use Red coloured batter & fill upto ¾ of the cup.
Bake for about 20 to 25 mins  or until baked well.
A tooth pick inserted to cake should come out clean when it is baked.
Once it is baked, transfer to cooling rack to cool down completely
Frosting

I used buttercream icing for decorating.
Used star tip & decorate it with a simple design.