Pre-heat oven to 180°C/160°C fan/Gas Mark 4. Place 12 fairy cake cases into a bun tin.
Cream together the margarine and sugar until light and fluffy.
Gradually beat in the eggs and Vanilla Extract, if the mixture starts to curdle, add a little flour.
Fold in the remaining flour with a metal spoon.
Divide the mixture into 4 bowls, add a different colour food gel to each bowl, add a few drops at a time until the desired colour is achieved. Make sure the colour is mixed thoroughly into the batter.
Add a dollop of each coloured batter into each fairy cake case. Place your cakes in the oven and bakes for 15-20 minutes until well risen and firm to the touch. Remove from oven, leave to cool on a cooling rack.
Once cooled, it's time to decorate. First up make the buttercream, beat your butter until softened, gradually beat in the icing sugar until your have a light fluffy buttercream. Finally add the Vanilla Extract and a few drops of Blue Colour Gel and mix thoroughly adding more Colour Gel until the desired blue colour is achieved. Palette the blue buttercream onto each cupcake, you can also use a spoon to smooth the buttercream onto the top of each cake.
Place a rainbow sweet onto each cupcakes to represent and rainbow (you may need to cut them slightly shorter, so they stand up) and add some mini marshmallows around the base to represent clouds. Your rainbow cupcakes are now ready to enjoy!