Marshmallow fondant is already awesome, but if you add jello to it you can make it even more delicious while coloring it at the same time! Jello seems to mix in really well with the powdered sugar and gives good results for taste and look.
I made only 2oz at a time and then multiplied it for a whole bag of marshmallows, but if you are wondering, here is what I did for each of the colors shown:
*I actually don't measure powdered sugar. I figure it is always going to take what it takes.