Make purple icing to decorate your cakes, cupcakes and buns with the simplest of supplies using homemade or shop-bought plain white icing as a base. It doesn't take much time or effort to create the exact colour you need. Add your colours slowly and you'll get exactly the right shade of purple.
Take 1/2 cup (or one bar) of room temperature butter and place it in a bowl and beat with an electric mixer until fluffy.
Add in 1/2 tsp of vanilla extract with 2 tbsp milk. Beat on high until blended. Add more milk if your icing is too stiff, one tablespoon at a time.
Place 1 cup of icing sugar into the butter mixture and beat until blended. Repeat until all the icing sugar is gone.
Beat until fluffy and then add 10 drops of red food colouring for every five drops of blue colouring. Blend. Add the colour until you achieve the hue of purple you'd like.
You may want to consider buying cake decorating icing colouring that comes in a paste. This will provide you with a rich, deep colour without having to add too much food colouring which may colour your guests' mouths.