Use a good, tasty cupcake recipe and a delicious buttercream icing. Not everyone is crazy about marshmallows but they can pull the petals off and have a wonderful cupcake underneath!
Use any colored sugar you like or multiple sugars. It would be pretty to do the petals in different shades of the same hue for an ombre effect.
You can color your own sugar! Just fill a small jar about half full with regular granulate sugar. Add a drop of food coloring at a time and shake, shake, shake! Add more food color to achieve a darker color, drop by drop. If you used gel food color, stir the mixture with a spoon instead of shaking. Keep pushing the sugar against the walls of the glass jar as you stir, till all the gel food color has been distributed.
It's fine to make all the marshmallow "petals" before you get started with the decorating but frost each cupcake as you go. If the icing hardens with will be more difficult for the marshmallow "petals" to adhere.
If you pinch the outer tips of "the petals" as you're placing them on the cupcake you'll get a different looking flower than if you keep them rounded.
This would be a really fun project to do with kids!