I'd recommend mixing and bagging each colour straight away, then snip the corner off the bag when you are ready to pipe each one, because the batter will dry out if it sits in the bowl. (pizzarossa.me)
Snip the corner of the nutella filling, and create a swirl pattern in the center of the pancake as pictured above. (layersofhappiness.com)
For an easy way to pipe the icing, put it in a ziplok bag and snip a corner for a piping bag! (thewimpyvegetarian.com)