Leave the butter in room temperature till soft.
In a neat bowl, cube the butter and start beating it slowly till fluffy.
Add the icing sugar little by little and keep beating till well incorporated and glossy. If you feel the buttercream is too thick, then add milk in tbsp to get the desired consistency.
Add desired colors (I used Wilton Green for 1/4 the quantity and Wilton Pink for the remaining).
Leave in the fridge to chill for around 20 minutes. Then use to decorate with tips and piping bags as desired.
To color the buttercream, dip a toothpick into your gel color and dip it back into the buttercream. Repeat with a different toothpick if you want a darker color. Fold well with a spatula.